Active Galaxies Active Galaxies and Quasars

Introduction: A Monster in the Middle

11 9-10 12 Most large galaxies have ~10 Mo of stars, ~10 Mo of interstellar gas, and ~10 Mo of dark matter. But some galaxies (certainly 5%, perhaps 10%? 50%? all??) also have something else...a monster in the middle! How can these incredible objects be explained? Long ago when galaxies were young, the stars in their cores were very closely packed. Star collisions and 6 9 mergers occurred, giving rise to a single massive black hole (MBH) with perhaps 10 - 10 Mo. Gas from the galaxy's interstellar medium, from a cannibalized galaxy, or from a star that strays too close, falls onto the MBH. As in X-ray binary star systems, an accretion disk forms, emitting huge amounts of light across the electromagnetic spectrum (infrared to gamma-rays). The MBH plus accretion disk produces the phenomena seen in active galactic nuclei (AGN). Below you see optical and radio images of the active galaxy NGC 4261. The central object, accretion disk, and lobes are all visible.

The different types of AGN are variations on this theme. Many galaxies today (including our Galactic center??) may have a quiet MBH which happens not to have recently accreted gas. Seyfert galaxies have accretion onto a moderate-mass MBH, while the more luminous quasi-stellar objects have accretion onto a high-mass MBH. In ~10% of the AGN, the MBH + accretion disk somehow produce narrow beams of energetic particles and magnetic fields, and eject them outward in opposite directions away from the disk. These are the radio jets, which emerge at nearly the speed of light. Radio galaxies, quasars, and blazars are AGN with strong jets, which can travel outward into large regions of intergalactic space. Many of the apparent differences between types of AGN are due to our having different orientations with respect to the disk.

http://imagine.gsfc.nasa.gov/docs/science/know_l2/active_galaxies.html (1 of 4) [5/26/1999 11:37:24 AM] Active Galaxies Considerable uncertainties remain. Exactly how are jets produced and accelerated? Where do the clouds producing the broad emission lines come from? Can we empirically confirm that a MBH is actually present?

Seyferts

Consider NGC 4151, a galaxy 15 Mpc away. Photographs by Carl Seyfert in the 1940s showed a very bright point-like nucleus. Its spectrum is very unusual: in addition to continua + absorption lines from normal stars, Seyfert galaxy nuclei have very strong emission lines. Some are common lines (e.g. H-alpha, H-beta) but others are weird (e.g. twice-ionized oxygen lines), requiring hot gas far out of equilibrium. The lines are very broad, requiring that the gas be Doppler shifted in all directions up to ~20,000 km/s. The nuclei vary in brightness on timescales of months, requiring them to be < 1 pc in size. The total 10 luminosity can be equivalent to 10 Lo! What is this bizarre object in the center of Seyfert's spiral galaxies? Later in the 1940s, astronomers began scanning the skies with radio telescopes. They found strange radio structures on opposite sides of radio galaxies, plus a tiny source of radio emission at the nucleus. The nuclei of these radio galaxies shoot out narrow beams of extremely energetic electrons and magnetic fields, producing radio synchrotron radiation. The radio components include: the compact core at the galaxy nucleus, jets, lobes, and a hot spot where the jet slams into the interstellar medium. Quasars

In the 1960s, some radio sources seemed to be associated with 'stars', and were called quasi-stellar radio sources or quasars. But they had spectra similar to Seyfert galaxy nuclei! It became clear that they are Seyferts and radio galaxies where the nucleus out shines all of the stars by factors of 10-1000. The 12 luminosity of quasars can reach 10 Lo. In the 1970-80s, findings include:

http://imagine.gsfc.nasa.gov/docs/science/know_l2/active_galaxies.html (2 of 4) [5/26/1999 11:37:24 AM] Active Galaxies 1. X-ray satellite telescopes found strong and very rapidly variable X-ray emission from Seyferts and quasars. Timescales for these variations were as short as days, hours, or even minutes. 2. Rare BL Lac objects and blazars were discovered. These are radio galaxies with jets pointing directly at us, ejected by the active nucleus at velocities near the speed of light! 3. Optical astronomers find thousands of faint distant quasars which are not radio-loud. Strangely, there were many more quasars early in the Universe than there are today. 4. In 1993, the Compton Gamma-Ray Observatory discovers incredibly intense gamma-rays from the jets of some blazars: Stronger than X-ray, optical, radio emission combined! Blazars

Active Galactic Nuclei observed at high (>100 MeV) energies form a subclass known as blazars; a blazar is believed to be an AGN which has one of its relativistic jets pointed toward the Earth so that the emission we observe is dominated by phenomena occurring in the jet region. Amongst all AGNs, blazars emit over the widest range of frequencies, being detected from radio to gamma-ray. Specifically, to be classified as a blazar an AGN must be seen with one of the following properties: ● high radio-brightness accompanied by flatness of the radio spectrum ● high optical polarization, ● strong optical variability on very short timescales (less than few days). In the class of objects selected according to these criteria, there appear to be two subgroups: (1) sources showing strong and broad emission lines, such as those of quasars (called Flat Spectrum Radio Quasars), and (2) sources showing a featureless optical spectrum (called BL Lac objects). There are additional important differences between these subclasses. such as they show different luminosity and redshift distributions, and a different morphology of the extended radio emission. Of the 80 blazars detected already by the EGRET experiment on board the Compton Gamma-Ray Observatory, most of them (about 80 %) are Flat Spectrum Radio Quasars (FSRQ), while the others have been identified as BL Lac objects.

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Imagine the Universe! Dictionary

Please allow the whole page to load before you start searching for an entry. Otherwise, errors will occur. [A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ] A accretion Accumulation of dust and gas into larger bodies such as stars, planets and moons. accretion disk A relatively flat sheet of gas and dust surrounding a newborn star, a black hole, or any massive object growing in size by attracting material. active galactic nuclei (AGN) It is believed that these are normal galaxies with a massive black hole accreting gas at its center, thus producing enormous amounts of energy at all wavelengths of the electromagnetic spectrum. Tell me about AGN! Tell me more about AGN! angstrom A unit of length equal to 0.00000001 centimeters. Scientists sometimes write this as 1 x 10-8 cm (see scientific notation). angular momentum A quantity obtained by multiplying the mass of an orbiting body by its velocity and the radius of its orbit. According to the conservation laws of physics, the angular momentum of any orbiting body must remain constant at all points in the orbit, i.e., it cannot be created or destroyed. If the orbit is elliptical the radius will vary. Since the mass is constant, the velocity changes. Thus planets in elliptical orbits travel faster at periastron and more slowly at apastron. A spinning body also possesses spin angular momentum. apoapsis The point in an orbit when the two objects are farthest apart. Special names are given to this orbital point for commonly used systems. For example, the point of greatest separation of two stars, as in a binary star orbit, is called apastron; the point in its orbit where a planet is farthest from the Sun is called aphelion; the point in its orbit where an Earth satellite is farthest from the Earth is called apogee. Ariel V

http://imagine.gsfc.nasa.gov/docs/dictionary.html (1 of 28) [5/26/1999 11:37:56 AM] Imagine the Universe! Dictionary A UK X-ray mission, also known as UK-5 Tell me more about Ariel V ASCA The Japanese Asuka spacecraft (formerly Astro-D) Tell me more about ASCA ASM All Sky Monitor. Many high-energy satellites have carried ASM detectors, including the ASM on Vela 5B, Ariel V, and the Rossi X-ray Timing Explorer. Astro E A new X-ray/gamma-ray mission being built jointly by the United States and Japan. Astro E currently has an estimated launch date of the year 2000. Tell me more about Astro E astronomical unit (AU) 149,597,870 km; the average distance from the Earth to the Sun. astronomy The scientific study of matter in outer space, especially the positions, dimensions, distribution, motion, composition, energy, and evolution of celestial bodies and phenomena. astrophysics The part of astronomy that deals principally with the physics of stars, stellar systems, and interstellar material. atmosphere The gas that surrounds a planet or star. The Earth's atmosphere is made up of mostly nitrogen, while the Sun's atmosphere consists of mostly hydrogen. AXAF The Advanced X-ray Astrophysics Facility. AXAF is currently scheduled to be launched by the Space Shuttle in August, 1998. Tell me more about AXAF B

Balmer lines (J. Balmer) Emission or absorption lines in the spectrum of hydrogen that arise from transitions between the second (or first excited) state and higher energy states of the hydrogen atom. BBXRT Broad Band X-Ray Telescope on Astro-1 shuttle flight (Dec. 1990) Tell me more about BBXRT

http://imagine.gsfc.nasa.gov/docs/dictionary.html (2 of 28) [5/26/1999 11:37:56 AM] Imagine the Universe! Dictionary binary stars Binary stars are two stars that orbit around a common center of mass. An X-ray binary is a special case where one of the stars is a collapsed object such as a white dwarf, neutron star, or black hole. Matter is stripped from the normal star and falls onto the collapsed star, producing X-rays. Tell me about X-ray binary stars Tell me more about X-ray binary stars black hole An object whose gravity is so strong that not even light can escape from it. Tell me about X-rays from black holes Tell me about gamma-rays from black holes and neutron stars Tell me more about black holes black-hole dynamic laws; laws of black-hole dynamics 1. First law of black hole dynamics: For interactions between black holes and normal matter, the conservation laws of mass-energy, electric charge, linear momentum, and angular momentum, hold. This is analogous to the first law of thermodynamics. 2. Second law of black hole dynamics: With black-hole interactions, or interactions between black holes and normal matter, the sum of the surface areas of all black holes involved can never decrease. This is analogous to the second law of thermodynamics, with the surface areas of the black holes being a measure of the entropy of the system. blackbody radiation The radiation -- the radiance at particular frequencies all across the spectrum -- produced by a blackbody -- that is, a perfect radiator (and absorber) of heat. Physicists had difficulty explaining it until Planck introduced his quantum of action. blackbody temperature The temperature of an object if it is re-radiating all the thermal energy that has been added to it; if an object is not a blackbody radiator, it will not re-radiate all the excess heat and the leftover will go toward increasing its temperature. blueshift An apparent shift toward shorter wavelengths of spectral lines in the radiation emitted by an object caused by the emitting object moving toward the observer. See also Doppler effect. Boltzmann constant; k (L. Boltzmann) A constant which describes the relationship between temperature and kinetic energy for molecules in an ideal gas. It is equal to 1.380622 x 10-23 J/K (see scientific notation). Brahe, Tycho 1546 - 1601 (a.k.a Tyge Ottesen) Danish astronomer whose accurate astronomical observations formed the basis for Johannes Kepler's laws of planetary motion. (132 k GIF)

http://imagine.gsfc.nasa.gov/docs/dictionary.html (3 of 28) [5/26/1999 11:37:56 AM] Imagine the Universe! Dictionary bremsstrahlung "braking radiation", the main way very fast charged particles lose energy when traveling through matter. Radiation is emitted when charged particles are accelerated. In this case, the acceleration is caused by the electromagnetic fields of the atomic nuclei of the medium. C calibration A process for translating the signals produced by a measuring instrument (such as a telescope) into something that is scientifically useful. This procedure removes most of the errors caused by environmental and instrumental instabilities. CGRO The Compton Gamma Ray Observatory Tell me more about CGRO Chandrasekhar limit (S. Chandrasekhar; 1910 - 1995) A limit which mandates that no white dwarf (a collapsed, degenerate star) can be more massive than about 1.4 solar masses. Any degenerate object more massive must inevitably collapse into a neutron star. cluster of galaxies A system of galaxies containing from a few to a few thousand member galaxies which are all gravitationally bound to each other. collecting area The amount of area a telescope has that is capable of collecting electromagnetic radiation. Collecting area is important for a telescope's sensitivity: the more radiation it can collect (that is, the larger its collecting area), the more sensitive it is to dim objects. Compton effect (A.H. Compton; 1923) An effect that demonstrates that photons (the quantum of electromagnetic radiation) have momentum. A photon fired at a stationary particle, such as an electron, will impart momentum to the electron and, since its energy has been decreased, will experience a corresponding decrease in frequency. Tell me how gamma-ray astronomers use the Compton effect Copernicus NASA ultraviolet/X-ray mission, also known as OAO-3 Tell me more about Copernicus Copernicus, Nicolaus 1473 - 1543 Polish astronomer who advanced the heliocentric theory that the Earth and other planets revolve around the Sun. This was highly controversial at the time as the Ptolemaic view of the universe, which was the prevailing theory for over 1000 years, was deeply ingrained in the prevailing philosophy and religion. (It should be noted, however, that the heliocentric idea was first put forth by Aristarcus of Samos in the 3rd century B.C., a fact known to Copernicus but long ignored.) (125 k GIF). corona (plural: coronae)

http://imagine.gsfc.nasa.gov/docs/dictionary.html (4 of 28) [5/26/1999 11:37:57 AM] Imagine the Universe! Dictionary The uppermost level of the solar atmosphere, characterized by low densities and high temperatures (> 1,000,000 degrees K). Tell me about X-rays from the Sun's corona Tell me about X-rays from other stellar coronae COS-B A satellite launched in August 1975 to study extraterrestrial sources of gamma-ray emission. Tell me more about COS-B cosmic background radiation; primal glow The background of radiation mostly in the frequency range 3 x 108 to 3 x 1011 Hz (see scientific notation) discovered in space in 1965. It is believed to be the cosmologically redshifted radiation released by the Big Bang itself. cosmic rays Atomic nuclei (mostly protons) and electrons that are observed to strike the Earth's atmosphere with exceedingly high energies. cosmological constant; Lambda The constant introduced to the Einstein field equation, intended to admit static cosmological solutions. At the time the current philosophical view was the steady-state model of the Universe, where the Universe has been around for infinite time. Early analysis of the field equation indicated that general relativity allowed dynamic cosmological models only (ones that are either contracting or expanding), but no static models. Einstein introduced the most natural aberration to the field equation that he could think of: the addition of a term proportional to the spacetime metric tensor, g, with the constant of proportionality being the cosmological constant: G + Lambda g = 8 pi T. Hubble's later discovery of the expansion of the Universe indicated that the introduction of the cosmological constant was unnecessary; had Einstein believed what his field equation was telling him, he could have claimed the expansion of the Universe as perhaps the greatest and most convincing prediction of general relativity; he called this the "greatest blunder of my life." cosmological distance A distance far beyond the boundaries of our Galaxy. When viewing objects at cosmological distances, the curved nature of spacetime could become apparent. Possible cosmological effects include time dilation and redshift. cosmological redshift An effect where light emitted from a distant source appears redshifted because of the expansion of spacetime itself. Compare Doppler effect. cosmology The astrophysical study of the history, structure, and constituent dynamics of the universe.

http://imagine.gsfc.nasa.gov/docs/dictionary.html (5 of 28) [5/26/1999 11:37:57 AM] Imagine the Universe! Dictionary D de Broglie wavelength (L. de Broglie; 1924) According to quantum mechanics all particles also have wave characteristics, where the wavelength of a particle is inversely proportional to its momentum and the constant of proportionality is the Planck constant. Declination A coordinate which, along with Right Ascension, may be used to locate any position in the sky. Declination is analogous to latitude for locating positions on the Earth. deconvolution An image processing technique that removes features in an image that are caused by the telescope itself rather than from actual light coming from the sky. density The amount of mass of any substance which can be contained in one cubic centimeter. Measured in grams per cubic centimeter (or kilograms per liter); the density of water is 1.0; iron is 7.9; lead is 11.3. disk (of planet or other object) The apparent circular shape that the Sun, a planet, or a moon displays when seen in the sky or through a telescope. Doppler effect (C.J. Doppler) The apparent change in wavelength of sound or light caused by the motion of the source, observer or both. Waves emitted by a moving object as received by an observer will be blueshifted (compressed) if approaching, redshifted (elongated) if receding. It occurs both in sound and light. How much the frequency changes depends on how fast the object is moving toward or away from the receiver. Compare cosmological redshift. E eccentric Non-circular; elliptical (applied to an orbit). eccentricity A value that defines the shape of an ellipse or planetary orbit. The eccentricity of an ellipse (planetary orbit) is the ratio of the distance between the foci and the major axis. Equivalently the eccentricity is (ra-rp)/(ra+rp) where ra is the apoapsis distance and rp is the periapsis distance. eclipse The cutting off, or blocking, of light from one celestial body by another. ecliptic The plane of Earth's orbit about the Sun Eddington limit (Sir A. Eddington) The theoretical limit at which the photon pressure would exceed the gravitational attraction of a

http://imagine.gsfc.nasa.gov/docs/dictionary.html (6 of 28) [5/26/1999 11:37:57 AM] Imagine the Universe! Dictionary light-emitting body. That is, a body emitting radiation at greater than the Eddington limit would break up from its own photon pressure. Einstein, Albert 1879 - 1955 German-American physicist; developed the Special and General Theories of Relativity which along with Quantum Mechanics is the foundation of modern physics. (32 k GIF) ejecta Material that is ejected. Used mostly to describe the content of a massive star that is propelled outward in a supernova explosion. electromagnetic spectrum The full range of frequencies, from radio waves to gamma-rays, that characterizes light. Introduce me to the electromagnetic spectrum Tell me more about the electromagnetic spectrum electromagnetic waves (radiation) Another term for light. Light waves are fluctuations of electric and magnetic fields in space. electron A particle commonly found in the outer layers of atoms with a negative charge. The electron has only 0.0005 the mass of the proton. electron volt The change of potential energy experienced by an electron moving from a place where the potential has a value of V to a place where it has a value of (V+1 volt). This is a convenient energy unit when dealing with the motions of electrons and ions in electric fields; the unit is also the one used to describe the energy of X-rays and gamma-rays. A keV (or kiloelectron volt) is equal to 1000 electron volts. An MeV is equal to one million electron volts. A GeV is equal to one billion (109) electron volts. A TeV is equal to a million million (1012) electron volts. elements The fundamental kinds of atoms that make up the building blocks of matter, which are each shown on the periodic table of the elements. The most abundant elements in the universe are hydrogen and helium. These two elements make up about 80and 20 % of all the matter in the universe respectively. Despite comprising only a very small fraction the universe, the remaining heavy elements can greatly influence astronomical phenomena. About 2 % of the Milky Way's disk is comprised of heavy elements. ellipse Oval. That the orbits of the planets are ellipses, not circles, was first discovered by Johannes Kepler based on the careful observations by Tycho Brahe. erg/sec A form of the metric unit for power. It is equal to 10-10 kilowatts (see scientific notation). event horizon The radius that a spherical mass must be compressed to in order to transform it into a black hole, or the radius at which time and space switch responsibilities. Once inside the event horizon, it is fundamentally

http://imagine.gsfc.nasa.gov/docs/dictionary.html (7 of 28) [5/26/1999 11:37:57 AM] Imagine the Universe! Dictionary impossible to escape to the outside. Furthermore, nothing can prevent a particle from hitting the singularity in a very short amount of proper time once it has entered the horizon. In this sense, the event horizon is a "point of no return". See Schwarzschild radius. evolved star A star near the end of its lifetime when most of its fuel has been used up. This period of the star's life is characterized by loss of mass from its surface in the form of a stellar wind. EXOSAT European Space Agency's X-ray Observatory Tell me more about EXOSAT extragalactic Outside of, or beyond, our own galaxy. F

Fast Fourier Transformation (FFT) A Fourier Transform is the mathematical operation that takes measurements made with a radio interferometer and transforms them into an image of the radio sky. The Fast Fourier Transform is technique used by computer programs that allows the Fourier Transform to be computed very quickly. Fermi acceleration In order to explain the origins of cosmic rays, Enrico Fermi (1949) introduced a mechanism of particle acceleration, whereby charged particles bounce off moving interstellar magnetic fields and either gain or lose energy, depending on whether the "magnetic mirror" is approaching or receding. In a typical environment, he argued, the probability of a head-on collision is greater than a head-tail collision, so particles would be accelerated on average. This random process is now called 2nd order Fermi acceleration, because the mean energy gain per "bounce" is dependent on the "mirror" velocity squared. Bell (1978) and Blandford and Ostriker (1978) independently showed that Fermi acceleration by supernova remnant (SNR) shocks is particularly efficient, because the motions are not random. A charged particle ahead of the shock front can pass through the shock and then be scattered by magnetic inhomogeneities behind the shock. The particle gains energy from this "bounce" and flies back across the shock, where it can be scattered by magnetic inhomogeneities ahead of the shock. This enables the particle to bounce back and forth again and again, gaining energy each time. This process is now called 1st order Fermi acceleration, because the mean energy gain is dependent on the shock velocity only to the first power. frequency A property of a wave that describes how many wave patterns or cycles pass by in a period of time. Frequency is often measured in Hertz (Hz), where a wave with a frequency of 1 Hz will pass by at 1 cycle per second. FTOOLS A suite of software tools developed at the OGIP for general and mission-specific manipulation of FITS files. FTP

http://imagine.gsfc.nasa.gov/docs/dictionary.html (8 of 28) [5/26/1999 11:37:57 AM] Imagine the Universe! Dictionary File Transfer Protocol -- A widely available method for transferring files over the Internet. G galactic halo A spherical region surrounding the center of a galaxy. This region may extend beyond the luminous boundaries of the galaxy and contain a significant fraction of the galaxy's mass. Compared to cosmological distances, objects in the halo of our galaxy would be very nearby. galaxy A component of our universe made up of gas and a large number (usually more than a million) of stars held together by gravity. Galilei, Galileo (1564 - 1642) An Italian scientist, Galileo was renowned for his epoch making contribution to physics, astronomy, and scientific philosophy. He is regarded as the chief founder of modern science. He developed the telescope, with which he found craters on the Moon and discovered the largest moons of Jupiter. Galileo was condemned by the Catholic Church for his view of the cosmos based on the theory of Copernicus. (14 k GIF) gamma-ray The highest energy, shortest wavelength electromagnetic radiations. Usually, they are thought of as any photons having energies greater than about 100 keV. gravitational collapse When a massive body collapses under its own weight. (For example, interstellar clouds collapse to become stars until the onset of nuclear fusion stops the collapse.) Gamma Ray Imaging Platform (GRIP) A balloon-borne gamma-ray telescope made by a group at the California Institute of Technology. It has had many successful flights. Gamma-Ray Imaging Spectrometer (GRIS) Gamma-Ray Burst (GRB) Plural is GRBs. A burst of gamma-rays from space lasting from a fraction of a second to many minutes. There is no clear scientific consensus as to their cause or even their distance. Tell me about Gamma-Ray Bursts Tell me more about Gamma-Ray Bursts general relativity The geometric theory of gravitation developed by Albert Einstein, incorporating and extending the theory of special relativity to accelerated frames of reference and introducing the principle that gravitational and inertial forces are equivalent. Giant Molecular Cloud (GMC) Massive clouds of gas in interstellar space composed primarily of hydrogen molecules (two hydrogen

http://imagine.gsfc.nasa.gov/docs/dictionary.html (9 of 28) [5/26/1999 11:37:57 AM] Imagine the Universe! Dictionary atoms bound together), though also containing other molecules observable by radio telescopes. These clouds can contain enough mass to make several million stars like our Sun and are often the sites of star formation. Ginga The third Japanese X-ray mission, also known as Astro-C. Tell me more about Ginga gravitational radius See event horizon. gravity A mutual physical force attracting two bodies. GSFC Goddard Space Flight Center guest star The ancient Chinese term for a star that newly appears in the night sky, and then later disappears. Later, the Europeans called this a nova. H

Hawking radiation (S.W. Hawking; 1973) The theory that black holes emit radiation like any other hot body. Virtual particle-antiparticle pairs are constantly being created in supposedly empty space. Occasionally, a pair will be created just outside the event horizon of a black hole. There are three possibilities: both particles are captured by the hole;1. both particles are captured by the hole;1. both particles escape the hole;2. both particles escape the hole;2. one particle escapes while the other is captured.3. one particle escapes while the other is captured.3. The first two cases are straightforward; the virtual particle-antiparticle pair recombine and return their energy back to the void via the uncertainty principle. It is the third case that interests us. In this case, one of the particles has escaped (and is speeding away to infinity), while the other has been captured by the hole. The escapee becomes real and can now be detected by distant observers. But the captured particle is still virtual; because of this, it has to restore conservation of energy by assigning itself a negative mass-energy. Since the hole has absorbed it, the hole loses mass and thus appears to shrink. From a distance, it appears as if the hole has emitted a particle and reduced in mass. The rate of power emission is proportional to the inverse square of the hole's mass; thus, the smaller a hole gets, the faster and faster it emits Hawking radiation. This leads to a runaway process; what happens when the hole gets very small is unclear; quantum theory seems to indicate that some kind of "remnant" might be left behind after the hole has emitted away all its mass-energy. Hawking temperature The temperature of a black hole caused by the emission of Hawking radiation.

http://imagine.gsfc.nasa.gov/docs/dictionary.html (10 of 28) [5/26/1999 11:37:57 AM] Imagine the Universe! Dictionary HEAO The High Energy Astrophysical Observatory satellite series Tell me more about HEAO-1 Tell me more about HEAO-2 (Einstein Observatory) Tell me more about HEAO-3 HEASARC High Energy Astrophysics Science Archive Research Center Herschel, Sir William (1738 - 1822) Sir William Herschel was a renowned astronomer who first detected the infrared region of the electromagnetic spectrum in 1800. Hertz, Heinrich (1857 - 1894) A German physics professor who did the first experiments with generating and receiving electromagnetic waves, in particular radio waves. In his honor, the units associated with measuring the cycles per second of the waves (or the number of times the tip-tops of the waves pass a fixed point in space in 1 second of time) is called the hertz. hertz; Hz (after H. Hertz, 1857 - 1894) The derived SI unit of frequency, defined as a frequency of 1 cycle per second. HST Hubble Space Telescope Hubble, Edwin P. 1889 - 1953 American astronomer whose observations proved that galaxies are "island universes", not nebulae inside our own galaxy. His greatest discovery was the linear relationship between a galaxy's distance and the speed with which it is moving. The Hubble Space Telescope is named in his honor. (58 k GIF)

Hubble constant; Ho (E.P. Hubble; 1925) The constant which determines the relationship between the distance to a galaxy and its velocity of recession due to the expansion of the Universe. Since the Universe is self-gravitating, it is not truly constant. In cosmology, it is defined as H = (da/dt)/a, where a is the 4-radius of the Universe. When evaluated for the present, it is written H0 = Hnow. The Hubble constant is not known to great accuracy (only within about a factor of 2), but is believed to lie somewhere between 50 and 100 km/s/Mpc. Hubble's law (E.P. Hubble; 1925) A relationship discovered between distance and radial velocity. The further away a galaxy is from us, the faster it is receding from us. The constant of proportionality is the Hubble constant, H_0. The cause is interpreted as the expansion of spacetime itself. Huygens, Christiaan (1629 - 1695) A Dutch physicist who was the leading proponent of the wave theory of light. He also made important

http://imagine.gsfc.nasa.gov/docs/dictionary.html (11 of 28) [5/26/1999 11:37:57 AM] Imagine the Universe! Dictionary contributions to mechanics, stating that in a collision between bodies, neither loses nor gains ``motion'' (his term for momentum). In astronomy, he discovered Titan (Saturn's largest moon) and was the first to correctly identify the observed elongation of Saturn as the presence of Saturn's rings. (88 k GIF) I

IKI Space Research Institute (Russia) implosion A violent inward collapse. An inward explosion. infrared Electromagnetic radiation at wavelengths longer than the red end of visible light and shorter than microwaves (roughly between 1 and 100 microns). Almost none of the infrared portion of the electromagnetic spectrum can reach the surface of the Earth, although some portions can be observed by high-altitude aircraft (such as the Kuiper Observatory) or telescopes on high mountaintops (such as the peak of Mauna Loa in Hawaii). inclination The inclination of a planet's orbit is the angle between the plane of its orbit and the ecliptic; the inclination of a moon's orbit is the angle between the plane of its orbit and the plane of its primary's equator. image In astronomy, a picture of the sky. Tell me about how astronomers use images interstellar medium The gas and dust between stars, which fills the plane of the Galaxy much like air fills the world we live in. For centuries, scientists believed that the space between the stars was empty. It wasn't until the eighteenth century, when William Herschel observed nebulous patches of sky through his telescope, that serious consideration was given to the notion that interstellar space was something to study. It was only in the last century that observations of interstellar material suggested that it was not even uniformly distributed through space, but that it had a unique structure. ions An atom with one or more electrons stripped off, giving it a net positive charge. ionic (or ionized) gas Gas whose atoms have lost or gained electrons, causing them to be electrically charged. In astronomy, this term is most often used to describe the gas around hot stars where the high temperature causes atoms to lose electrons. IUE International Ultraviolet Explorer

http://imagine.gsfc.nasa.gov/docs/dictionary.html (12 of 28) [5/26/1999 11:37:57 AM] Imagine the Universe! Dictionary J jets Beams of particles, usually coming from an active galactic nucleus or a pulsar. Unlike a jet airplane, when the stream of gas is in one direction, astrophysical jets come in pairs with each jet aiming in opposite directions. K kelvin (after Lord Kelvin, 1824 - 1907) A temperature scale often used in sciences such as astronomy. The fundamental SI unit of thermodynamic temperature defined as 1/273.16 of the thermodynamic temperature of the triple point of water. The Kelvin temperature scale is just like the Celsius scale except that the freezing point of water, zero degrees Celsius, is equal to 273 degrees Kelvin. [ K = C + 273o => F = 9/5C + 32o] Kepler, Johannes 1571 - 1630 German astronomer and mathematician. Considered a founder of modern astronomy, he formulated the famous three laws of planetary motion. They comprise a quantitative formulation of Copernicus's theory that the planets revolve around the Sun. (71 k GIF) Kepler's laws (J. Kepler) Kepler's first law A planet orbits the Sun in an ellipse with the Sun at one focus. Kepler's second law A ray directed from the Sun to a planet sweeps out equal areas in equal times. Kepler's third law The square of the period of a planet's orbit is proportional to the cube of that planet's semimajor axis; the constant of proportionality is the same for all planets. kilogram (kg) One kilogram is equivalent to 1,000 grams or 2.2 pounds; the mass of a liter of water. The fundamental SI unit of mass, it is the only SI unit still maintained by a physical artifact: a platinum-iridium bar kept in the International Bureau of Weights and Measures at Sevres, France. kinematics Refers to the calculation or description of the underlying mechanics of motion of an astronomical object. For example, in radioastronomy, spectral line graphs are used to determine the kinematics or relative motions of material at the center of a galaxy or surrounding a star as it is born. Kirchhoff's law of radiation (G.R. Kirchhoff) The emissivity of a body is equal to its absorbance at the same temperature. Kirchhoff's laws (G.R. Kirchhoff) Kirchhoff's first law An incandescent solid or gas under high pressure will produce a continuous spectrum.

http://imagine.gsfc.nasa.gov/docs/dictionary.html (13 of 28) [5/26/1999 11:37:57 AM] Imagine the Universe! Dictionary Kirchhoff's second law A low-density gas will radiate an emission-line spectrum with an underlying emission continuum. Kirchhoff's third law Continuous radiation viewed through a low-density gas will produce an absorption-line spectrum. L

L0 A representation of the luminosity of an object in terms of Solar luminosity. The average luminosity of the Sun is about 4x1033 erg/sec. Astronomers often express units for other objects in terms of solar units...it makes the resulting numbers smaller and easier to deal with. Lagrange, Joseph (1736 - 1813) A French mathematician of the eighteenth century. His work Mecanique Analytique (Analytical Mechanics; 1788) was a mathematical masterpiece. It contained clear, symmetrical notation and covered almost every area of pure mathematics. Lagrange developed the calculus of variations, established the theory of differential equations, and provided many new solutions and theorems in number theory. His classic Theorie des fonctions analytiques laid some of the foundations of group theory. Lagrange also invented the method of solving differential equations known as variation of parameters. (54 k GIF) Lagrange points Points in the vicinity of two massive bodies (such as the Earth and the Moon) where each others' respective gravities balance. There are five, labeled L1 through L5. L1, L2, and L3 lie along the centerline between the centers of mass between the two masses; L1 is on the inward side of the secondary, L2 is on the outward side of the secondary; and L3 is on the outward side of the primary. L4 and L5, the so-called Trojan points, lie along the orbit of the secondary around the primary, sixty degrees ahead and behind of the secondary. L1 through L3 are points of unstable equilibrium; any disturbance will move a test particle there out of the Lagrange point. L4 and L5 are points of stable equilibrium, provided that the mass of the secondary is less than about 1/25.96 the mass of the primary. These points are stable because centrifugal pseudo-forces work against gravity to cancel it out. laser Laser is an acronym for Light Amplification by Stimulated Emission of Radiation. It's a device that produces a coherent beam of optical radiation by stimulating electronic, ionic, or molecular transitions to higher levels so that when they return to lower energy levels they emit energy. LHEA Laboratory for High Energy Astrophysics (GSFC, Code 660) light Electromagnetic radiation that is visible to the human eye. light curve A graph that displays the time variation in light or magnitude of a variable or eclipsing star. Tell me about light curves

http://imagine.gsfc.nasa.gov/docs/dictionary.html (14 of 28) [5/26/1999 11:37:58 AM] Imagine the Universe! Dictionary light year A unit of length used in astronomy which equals the distance light travels in a year. At the rate of 300,000 kilometers per second (671 million miles per hour), 1 light-year is equivalent to 9.46053 x 1012 km, 5,880,000,000,000 miles or 63,240 AU (see scientific notation). limb The outer edge of the apparent disk of a celestial body. M

M0 A representation of the mass of an object in terms of Solar mass. The average mass of the Sun is about 2x1033 grams. Astronomers often express units for other objects in terms of solar units...it makes the resulting numbers smaller and easier to deal with. magnetic field A condition found in the region around a magnet or an electric current, characterized by the existence of a detectable magnetic force at every point in the region. magnetic pole Either of two limited regions in a magnet at which the magnet's field is most intense. magnetosphere The region of space in which the magnetic field of an object (e.g., a star or planet) dominates the radiation pressure of the stellar wind to which it is exposed. magnetotail The portion of a planetary magnetosphere which is pushed in the direction of the solar wind. magnitude The degree of brightness of a celestial body designated on a numerical scale, on which the brightest star has magnitude -1.4 and the faintest visible star has magnitude 6, with the scale rule such that a decrease of one unit represents an increase in apparent brightness by a factor of 2.512; also called apparent magnitude. mass A measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies. matter A word used for any kind of stuff which contains mass. mega-ton A unit of energy used to describe nuclear warheads. The same amount energy as 1 million tons of TNT. 1 mega-ton = 4 x 1016 ergs = 4 x 109 joules. meter; m The fundamental SI unit of length, defined as the length of the path traveled by light in vacuum during a period of 1/299 792 458 s. A unit of length equal to about 39 inches. A kilometer is equal to 1000 meters.

http://imagine.gsfc.nasa.gov/docs/dictionary.html (15 of 28) [5/26/1999 11:37:58 AM] Imagine the Universe! Dictionary microwave Electromagnetic radiation which has a long wavelength (between 1 mm and 30 cm). Microwaves can be used to study the Universe, communicate with satellites in Earth orbit, and cook popcorn. N nebula A diffuse mass of interstellar dust and gas. neutrino A fundamental particle produced in massive numbers by the nuclear reactions in stars; they are very hard to detect because the vast majority of them pass completely through the Earth without interacting. neutron A particle commonly found in the nucleus of atoms with approximately the mass of a proton, but zero charge. neutron star The imploded core of a massive star produced by a supernova explosion. (typical mass of 1.4 times the mass of the Sun, radius of about 5 miles, density of a neutron.) According to astronomer and author Frank Shu, "A sugar cube of neutron-star stuff on Earth would weigh as much as all of humanity!" Neutron stars can be observed as pulsars.

Tell me about X-rays from neutron stars Tell me about gamma-rays from black holes and neutron stars Newton, Isaac 1642 - 1727 English cleric and scientist; discovered the classical laws of motion and gravity; the bit with the apple is probably apocryphal. (32 k GIF) Newton's law of universal gravitation (Sir I. Newton) Two bodies attract each other with equal and opposite forces; the magnitude of this force is proportional to the product of the two masses and is also proportional to the inverse square of the distance between the centers of mass of the two bodies. Newton's laws of motion (Sir I. Newton) Newton's first law of motion A body continues in its state of constant velocity (which may be zero) unless it is acted upon by an external force. Newton's second law of motion For an unbalanced force acting on a body, the acceleration produced is proportional to the force impressed; the constant of proportionality is the inertial mass of the body. Newton's third law of motion In a system where no external forces are present, every action force is always opposed by an equal and opposite reaction

http://imagine.gsfc.nasa.gov/docs/dictionary.html (16 of 28) [5/26/1999 11:37:58 AM] Imagine the Universe! Dictionary noise The random fluctuations that are always associated with a measurement that is repeated many times over. Noise appears in astronomical images as fluctuations in the image background. These fluctuations do not represent any real sources of light in the sky, but rather are caused by the imperfections of the telescope. If the noise is too high, it may obscure the dimmest objects within the field of view. nova (plural: novae) A star that experiences a sudden outburst of radiant energy, temporarily increasing its luminosity by hundreds to thousands of times before fading back to its original luminosity. nuclear fusion A nuclear process whereby several small nuclei are combined to make a larger one whose mass is slightly smaller than the sum of the small ones. The difference in mass is converted to energy by Einstein's famous equivalence "Energy = Mass times the Speed of Light squared". This is the source of the Sun's energy. O occultation The blockage of light by the intervention of another object; a planet can occult (block) the light from a distant star. opacity A property of matter that prevents light from passing through it; non-transparent. The opacity or opaqueness of something depends on the frequency of the light. For instance, the atmosphere of Venus is transparent to ultraviolet light, but is opaque to visual light. orbit The path of an object that is moving around a second object or point. OSO 3 Orbiting Solar Observatory 3 Tell me more about OSO 3 OSO 8 Orbiting Solar Observatory 8 Tell me more about OSO 8 P pair production The physical process whereby a gamma-ray photon, usually through an interaction with the electromagnetic field of a nucleus, produces an electron and an anti-electron (positron). The original photon no longer exists, its energy having gone to the two resulting particles. The inverse process, pair annihilation, creates two gamma-ray photons from the mutual destruction of an electron/positron pair. Tell me how astronomers use pair production

http://imagine.gsfc.nasa.gov/docs/dictionary.html (17 of 28) [5/26/1999 11:37:58 AM] Imagine the Universe! Dictionary parallax The angle between the two straight lines that join a celestial body to two different points of observation; e.g., two different points on the Earth as it moves through space. parsec A large distance often used in astronomy, it is equal to 3.26 light years, or 3.1 x 1018 cm (see scientific notation). A kiloparsec (kpc) is equal to 1000 parsecs. A megaparsec (Mpc) is equal to a million (106) parsecs. An object is at a distance of 1 parsec from us if its parallax is 1 second of arc. periapsis The point in the orbit closest to the planet. periastron The point of closest approach of two stars, as in a binary star orbit. perigee The point in the orbit closest to the Earth. perihelion The point in its orbit where a planet is closest to the Sun. when referring to objects orbiting the Earth the term perigee is used; the term periapsis is used for orbits around other bodies. (opposite of aphelion) photoelectric effect An effect explained by A. Einstein which demonstrates that light seems to be made up of particles, or photons. Light can excite electrons (called photoelectrons in this context) to be ejected from a metal. Light with a frequency below a certain threshold, at any intensity, will not cause any photoelectrons to be emitted from the metal. Above that frequency, photoelectrons are emitted in proportion to the intensity of incident light. The reason is that a photon has energy in proportion to its wavelength, and the constant of proportionality is the Planck constant. Below a certain frequency -- and thus below a certain energy -- the incident photons do not have enough energy to knock the photoelectrons out of the metal. Above that threshold energy, called the work function, photons will knock the photoelectrons out of the metal, in proportion to the number of photons (the intensity of the light). At higher frequencies and energies, the photoelectrons ejected obtain a kinetic energy corresponding to the difference between the photon's energy and the work function. pi The constant equal to the ratio of the circumference of a circle to its diameter, which is approximately 3.141593. Planck constant; h The fundamental constant equal to the ratio of the energy of a quantum of energy to its frequency. It is the quantum of action. It has the value 6.626196 x 10-34 J s (see scientific notation). Planck equation The quantum mechanical equation relating the energy of a photon E to its frequency nu:

http://imagine.gsfc.nasa.gov/docs/dictionary.html (18 of 28) [5/26/1999 11:37:58 AM] Imagine the Universe! Dictionary E = h x nu planetary nebula A shell of gas ejected from, and expanding about, a certain kind of extremely hot star. plasma A low-density gas in which the individual atoms are ionized (and therefore charged), even though the total number of positive and negative charges is equal, maintaining an overall electrical neutrality. pointing The direction in the sky to which the telescope is pointed. Pointing also describes how accurately a telescope can be pointed toward a particular direction in the sky. polarization A special property of light; light has three properties, brightness, color and polarization. Polarization is a condition in which the planes of vibration of the various rays in a light beam are at least partially aligned. positron The antiparticle to the electron. The positron has most of the same characteristics as an electron except it is positively charged. proton A particle commonly found in the nucleus of atoms with a positive charge. protostar Very dense regions (or cores) of molecular clouds where stars are in the process of forming. Ptolemy (ca. 100-ca. 170) A.k.a.Claudius Ptolemaeus. Ptolemy believed the planets and Sun to orbit the Earth in the order Mercury, Venus, Sun, Mars, Jupiter, Saturn. This system became known as the Ptolemaic system and predicted the positions of the planets accurately enough for naked-eye observations (although it made some ridiculous predictions, such as that the distance to the moon should vary by a factor of two over its orbit). He authored a book called Mathematical Syntaxis (widely known as the Almagest). The Almagest included a star catalog containing 48 constellations, using the names we still use today. (10 k GIF) pulsar A rotating neutron star which generates regular pulses of radiation. Pulsars were discovered by observations at radio wavelengths but have since been observed at optical, X-ray, and gamma-ray energies. Tell me about pulsars! Tell me more about pulsars! PVO Pioneer Venus Orbiter Tell me more about PVO

http://imagine.gsfc.nasa.gov/docs/dictionary.html (19 of 28) [5/26/1999 11:37:58 AM] Imagine the Universe! Dictionary Q quasar A specific type of quasi-stellar source. quasi-stellar source (QSS) Sometimes also called quasi-stellar object (QSO); A stellar-appearing object of very large redshift that is a strong source of radio waves; presumed to be extragalactic and highly luminous. R radial velocity The speed at which an object is moving away or toward an observer. By observing spectral lines, astronomers can determine how fast objects are moving away from or toward us; however, these spectral lines cannot be used to measure how fast the objects are moving across the sky. radian; rad The supplementary SI unit of angular measure, defined as the central angle of a circle whose subtended arc is equal to the radius of the circle. radiation Energy radiated in the form of waves or particles; photons. radiation belt Regions of charged particles in a magnetosphere. radio Electromagnetic radiation which has the lowest frequency, the longest wavelength, and is produced by charged particles moving back and forth; the atmosphere of the Earth is transparent to radio waves with wavelengths from a few millimeters to about twenty meters. Rayleigh criterion; resolving power A criterion for how finely a set of optics may be able to distinguish. It begins with the assumption that the central ring of one image should fall on the first dark ring of another image; for an objective lens with diameter d and employing light with a wavelength lambda (usually taken to be 560 nm), the resolving power is approximately given by 1.22 x lambda/d Rayleigh-Taylor instabilities Rayleigh-Taylor instabilities occur when a heavy (more dense) fluid is pushed against a light fluid -- like trying to balance water on top of air by filling a glass 1/2 full and carefully turning it over. Rayleigh-Taylor instabilities are important in many astronomical objects, because the two fluids trade places by sticking "fingers" into each other. These "fingers" can drag the magnetic field lines along with them, thus both enhancing and aligning the magnetic field. This result is evident in the example of a supernova remnant in the diagram below, from Chevalier (1977):

http://imagine.gsfc.nasa.gov/docs/dictionary.html (20 of 28) [5/26/1999 11:37:58 AM] Imagine the Universe! Dictionary

red giant A star that has low surface temperature and a diameter that is large relative to the Sun. redshift An apparent shift toward longer wavelengths of spectral lines in the radiation emitted by an object caused by the emitting object moving away from the observer. See also Doppler effect. reflection law For a wavefront intersecting a reflecting surface, the angle of incidence is equal to the angle of reflection, in the same plane defined by the ray of incidence and the normal. relativity principle The principle, employed by Einstein's relativity theories, that the laws of physics are the same, at least locally, in all coordinate frames. This principle, along with the principle of the constancy of the speed of light, constitutes the founding principles of special relativity. relativity, theory of More accurately describes the motions of bodies in strong gravitational fields or at near the speed of light than Newtonian mechanics. All experiments done to date agree with relativity's predictions to a high degree of accuracy. (Curiously, Einstein received the Nobel prize in 1921 not for Relativity but rather for his 1905 work on the photoelectric effect.) resolution (spatial) In astronomy, the ability of a telescope to differentiate between two objects in the sky which are separated by a small angular distance. The closer two objects can be while still allowing the telescope to see them as two distinct objects, the higher the resolution of the telescope. resolution (spectral or frequency) Similar to spatial resolution except that it applies to frequency, spectral resolution is the ability of the telescope to differentiate two light signals which differ in frequency by a small amount. The closer the two signals are in frequency while still allowing the telescope to separate them as two distinct components, the higher the spectral resolution of the telescope. resonance A relationship in which the orbital period of one body is related to that of another by a simple integer fraction, such as 1/2, 2/3, 3/5. retrograde The rotation or orbital motion of an object in a clockwise direction when viewed from the north pole of the ecliptic; moving in the opposite sense from the great majority of solar system bodies. Right Ascension A coordinate which, along with declination, may be used to locate any position in the sky. Right ascension

http://imagine.gsfc.nasa.gov/docs/dictionary.html (21 of 28) [5/26/1999 11:37:58 AM] Imagine the Universe! Dictionary is analogous to longitude for locating positions on the Earth. Ritter, Johann Wilhelm (1776 - 1810) Ritter is credited with discovering and investigating the ultraviolet region of the electromagnetic spectrum. Roche limit The smallest distance from a planet or other body at which purely gravitational forces can hold together a satellite or secondary body of the same mean density as the primary; at less than this distance the tidal forces of the primary would break up the secondary. Roche lobe The volume around a star in a binary system in which, if you were to release a particle, it would fall back onto the surface of that star. A particle released above the Roche lobe of either star will, in general, occupy the `circumbinary' region that surrounds both stars. The point at which the Roche lobes of the two stars touch is called the inner Lagrangian or L1 point. If a star in a close binary system evolves to the point at which it `fills' its Roche lobe, theoretical calculations predict that material from this star will overflow both onto the companion star (via the L1 point) and into the circumbinary environment. Röntgen, Wilhelm Conrad (1845 - 1923) A German scientist who fortuitously discovered X-rays in 1895. (43 k GIF). ROSAT Röntgen Satellite Tell me more about ROSAT S

SAS-2 The second Small Astronomy Satellite: a NASA satellite launched November 1972 with a mission dedicated to gamma-ray astronomy. Tell me more about SAS-2 SAS-3 The third Small Astronomy Satellite: a NASA satellite launched May 1975 to determine the location of bright X-ray sources and search for X-ray novae and other transient phenomena. Tell me more about SAS-3 satellite A body that revolves around a larger body. Schwarzschild radius The radius r of the event horizon for a Schwarzschild black hole. scientific notation A compact format for writing very large or very small numbers, most often used in scientific fields. The notation separates a number into two parts: a decimal fraction, usually between 1 and 10, and a power of ten. Thus 1.23 x 104 means 1.23 times 10 to the fourth power or 12,300; 5.67 x 10-8 means 5.67 divided

http://imagine.gsfc.nasa.gov/docs/dictionary.html (22 of 28) [5/26/1999 11:37:58 AM] Imagine the Universe! Dictionary by 10 to the eighth power or 0.0000000567. second; s The fundamental SI unit of time, defined as the period of time equal to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom. A nanosecond is equal to one-billionth (10-9) of a second. semimajor axis The semimajor axis of an ellipse (e.g. a planetary orbit) is 1/2 the length of the major axis which is a segment of a line passing thru the foci of the ellipse with endpoints on the ellipse itself. The semimajor axis of a planetary orbit is also the average distance from the planet to its primary. The periapsis and apoapsis distances can be calculated from the semimajor axis and the eccentricity by rp = a(1-e) and ra = a(1+e). sensitivity A measure of how bright objects need to be in order for that telescope to detect these objects. A highly sensitive telescope can detect dim objects, while a telescope with low sensitivity can detect only bright ones. Seyfert galaxy A spiral galaxy whose nucleus shows bright emission lines; one of a class of galaxies first described by C. Seyfert. shock wave A strong compression wave where there is a sudden change in gas velocity, density, pressure and temperature. singularity The center of a black hole, where the curvature of spacetime is maximal. At the singularity, the gravitational tides diverge; no solid object can even theoretically survive hitting the singularity. Although singularities generally predict inconsistencies in theory, singularities within black holes do not necessarily imply that general relativity is incomplete so long as singularities are always surrounded by event horizons. A proper formulation of quantum gravity may well avoid the classical singularity at the centers of black holes. solar flares Violent eruptions of gas on the Sun's surface. solar mass 33 A unit of mass equivalent to the mass of the Sun. 1 solar mass = 1 Msun = 2 x 10 grams. special relativity The physical theory of space and time developed by Albert Einstein, based on the postulates that all the laws of physics are equally valid in all frames of reference moving at a uniform velocity and that the speed of light from a uniformly moving source is always the same, regardless of how fast or slow the source or its observer is moving. The theory has as consequences the relativistic mass increase of rapidly moving objects, gravitational sources bending light, time dilatation, and the principle of mass-energy equivalence.

http://imagine.gsfc.nasa.gov/docs/dictionary.html (23 of 28) [5/26/1999 11:37:58 AM] Imagine the Universe! Dictionary See also general relativity. spectral line Light given off at a specific frequency by an atom or molecule. Every different type of atom or molecule gives off light at its own unique set of frequencies; thus, astronomers can look for gas containing a particular atom or molecule by tuning the telescope to one of its characteristic frequencies. For example, carbon monoxide (CO) has a spectral line at 115 Gigahertz (or a wavelength of 2.7 mm). spectrometer The instrument connected to a telescope that separates the light signals into different frequencies, producing a spectrum. A Diversive Spectrometer is like a prism. It scatters the X-rays of different energies to different places. We measure the energy by noting where the X-rays go. A Non-Dispersive Spectrometer measures the energy directly. spectroscopy The study of spectral lines from different atoms and molecules. Spectroscopy is an important part of studying the chemistry that goes on in stars and in interstellar clouds. spectrum (plural: spectra) A plot of the intensity of light at different frequencies. Or the distribution of wavelengths and frequencies. Tell me more about spectra speed of light (in vacuo); c The speed at which electromagnetic radiation propagates in a vacuum; it is defined as 299 792 458 m/s (186,000 miles/second). Einstein's Theory of Relativity implies that nothing can go faster than the speed of light. star A large ball of gas that creates and emits its own radiation. star cluster A bunch of stars (ranging in number from a few to hundreds of thousands) which are bound to each other by their mutual gravitational attraction. Stefan-Boltzmann constant; sigma (Stefan, L. Boltzmann) The constant of proportionality present in the Stefan-Boltzmann law. It is equal to 5.6697 x 10-8 Watts per square meter per degree Kelvin to the fourth power (see scientific notation). Stefan-Boltzmann law (Stefan, L. Boltzmann) The radiated power P (rate of emission of electromagnetic energy) of a hot body is proportional to the radiating surface area, A, and the fourth power of the thermodynamic temperature, T. The constant of proportionality is the Stefan-Boltzmann constant. stellar classification Stars are given a designation consisting of a letter and a number according to the nature of their spectral lines which corresponds roughly to surface temperature. The classes are: O, B, A, F, G, K, and M; O stars are the hottest; M the coolest. The numbers are simply subdivisions of the major classes. The classes are

http://imagine.gsfc.nasa.gov/docs/dictionary.html (24 of 28) [5/26/1999 11:37:59 AM] Imagine the Universe! Dictionary oddly sequenced because they were assigned long ago before we understood their relationship to temperature. O and B stars are rare but very bright; M stars are numerous but dim. The Sun is designated G2. stellar wind The ejection of gas off the surface of a star. Many different types of stars, including our Sun, have stellar winds; however, a star's wind is strongest near the end of its life when it has consumed most of its fuel. steradian; sr The supplementary SI unit of solid angle defined as the solid central angle of a sphere that encloses a surface on the sphere equal to the square of the sphere's radius. supernova (plural: supernovae) The death explosion of a massive star, resulting in a sharp increase in brightness followed by a gradual fading. At peak light output, supernova explosions can outshine a galaxy. The outer layers of the exploding star are blasted out in a radioactive cloud. This expanding cloud, visible long after the initial explosion fades from view, forms a supernova remnant (SNR). Tell me about X-rays from supernovae and their remnants Tell me about gamma-rays from supernovae Tell me more about supernovae Tell me more about supernova remnants sunspots Cooler (and thus darker) regions on the sun where the magnetic field loops up out of the solar surface. SXG The Spectrum X-Gamma mission Tell me more about SXG synchronous rotation Said of a satellite if the period of its rotation about its axis is the same as the period of its orbit around its primary. This implies that the satellite always keeps the same hemisphere facing its primary (e.g. the Moon). It also implies that one hemisphere (the leading hemisphere) always faces in the direction of the satellite's motion while the other (trailing) one always faces backward. synchrotron radiation Electromagnetic radiation given off when very high energy electrons encounter magnetic fields. Systéme Internationale d'Unités (SI) The coherent and rationalized system of units, derived from the MKS system (which itself is derived from the metric system), in common use in physics today. The fundamental SI unit of length is the meter, of time is the second, and of mass is the kilogram.

http://imagine.gsfc.nasa.gov/docs/dictionary.html (25 of 28) [5/26/1999 11:37:59 AM] Imagine the Universe! Dictionary T

Tenma The second Japanese X-ray mission, also known as Astro-B. Tell me more about Tenma Thomson, William 1824 - 1907 Also known as Lord Kelvin, the British physicist who developed the Kelvin scale of temperature and who supervised the laying of a trans-Atlantic cable. (11 k GIF) time dilation Stretching of time produced by relativity. Time dilation is a predicted effect of the cosmological paradigm. U

Uhuru NASA's first Small Astronomy Satellite, also known as SAS-1. Uhuru was launched from Kenya on 12 December, 1970; The seventh anniversary of Kenya's independence. The satellite was named "Uhuru" (Swahili for "freedom") in honor of its launch date. Tell me more about Uhuru ultraviolet Electromagnetic radiation at wavelengths shorter than the violet end of visible light; the atmosphere of the Earth effectively blocks the transmission of most ultraviolet light. universal constant of gravitation; G The constant of proportionality in Newton's law of universal gravitation and which plays an analogous role in A. Einstein's general relativity. It is equal to 6.664 x 10-11 newtons per square meter per kilogram squared (see scientific notation). V

Vela 5B US Atomic Energy Commission (now the Department of Energy) satellite with an all-sky X-ray monitor Tell me more about Vela 5B The Venera satellite series The Venera satellites were a series of probes (fly-bys and landers) sent by the Soviet Union to the planet Venus. Several Venera satellites carried high-energy astrophysics detectors. Tell me more about Venera 11 & 12 Tell me more about Venera 13 & 14 visible Electromagnetic radiation at wavelengths which the human eye can see. We perceive this radiation as

http://imagine.gsfc.nasa.gov/docs/dictionary.html (26 of 28) [5/26/1999 11:37:59 AM] Imagine the Universe! Dictionary colors ranging from red (longer wavelengths; ~ 700 nanometers) to violet (shorter wavelengths; ~400 nanometers.) W wave-particle duality The principle of quantum mechanics which implies that light (and, indeed, all other subatomic particles) sometimes act like a wave, and sometimes act like a particle, depending on the experiment you are performing. For instance, low frequency electromagnetic radiation tends to act more like a wave than a particle; high frequency electromagnetic radiation tends to act more like a particle than a wave. wavelength A property of a wave that gives the length between two peaks of the wave. white dwarf A star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size. Typically, a white dwarf has a radius equal to about 0.01 times that of the Sun, but it has a mass roughly equal to the Sun's. This gives a white dwarf a density about 1 million times that of water! Tell me more about white dwarfs Wien's displacement law For a blackbody, the product of the wavelength corresponding to the maximum radiancy and the thermodynamic temperature is a constant. As a result, as the temperature rises, the maximum of the radiant energy shifts toward the shorter wavelength (higher frequency and energy) end of the spectrum. WWW The World Wide Web -- a loose linkage of Internet sites which provide data and other services from around the world. X

X-ray Electromagnetic radiation of very short wavelength and very high-energy; X-rays have shorter wavelengths than ultraviolet light but longer wavelengths than cosmic rays. XSELECT A high-level tool to manage the FTOOLs XTE X-ray Timing Explorer, also known as the Rossi X-ray Timing Explorer (RXTE) Tell me more about RXTE

http://imagine.gsfc.nasa.gov/docs/dictionary.html (27 of 28) [5/26/1999 11:37:59 AM] Imagine the Universe! Dictionary Y Z

[A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ]

Ask a Other The Imagine! Imagine! Imagine Satellites Teachers NASA Good Imagine Homepage Feedback Science! & Data Corner Scientist Resources Dictionary

http://imagine.gsfc.nasa.gov/docs/dictionary.html (28 of 28) [5/26/1999 11:37:59 AM] Active Galaxies: Quiz

Active Galaxies Quiz

1. What kind of object is believed to be in the center of an active galaxy? [A] A radio telescope [B] A massive black hole [C] The Loch Ness monster 2. What features did Carl Seyfert observe in NGC 4151? [A] It contained H-alpha and H-beta lines [B] NGC 4151 had a bright point-like nucleus [C] It had the continuum lines from normal stars [D] All of the above 3. It is possible to have a 109 solar-mass black hole. [A] True [B] False [C] We don't know 4. What produces the phenomena observed in AGN? [A] A massive black hole plus an accretion disk [B] Grey-headed trolls [C] The solar cycle 5. What is the source of many of the apparent differences in the types of AGN we observe? [A] The size of the central black hole [B] How far away the galaxy is [C] The difference in our viewing angle of the accretion disk

http://imagine.gsfc.nasa.gov/docs/science/quiz_l2/active_galaxies_quiz.html (1 of 2) [5/26/1999 11:38:10 AM] Active Galaxies: Quiz Ask a Other The Imagine! Imagine! Imagine Satellites Teachers NASA Good Imagine Homepage Feedback Science! & Data Corner Scientist Resources Dictionary

http://imagine.gsfc.nasa.gov/docs/science/quiz_l2/active_galaxies_quiz.html (2 of 2) [5/26/1999 11:38:10 AM] Active Galaxy Cool Fact Active Galaxies

Cygnus A is one of the brightest radio sources in the sky. However, the galaxy itself is merely a tiny dot between two huge radio-emitting clouds that it has blasted out into space. The image on the left is the active galaxy Cygnus A in optical light. The image on the right is Cyg A in the radio band. One of the strongest radio sources in the sky, the galaxy itself is the tiny dot between the two huge lobes which have been blasted out into space.

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http://imagine.gsfc.nasa.gov/docs/science/know_l2/cool_active_fact.html [5/26/1999 11:38:24 AM] Imagine the Universe! Lesson Plans

Imagine the Universe! Lesson Plans

The following Lesson Plans are available/under development:

Grade Subject Math Standard Science Standard Title Level

Patterns & What's the Functions Math 6-8 Science as Inquiry Frequency, Roy Algebra G. Biv? Statistics

Algebra Science as Inquiry Time That Math 6-8 Statistics Motions & Forces Period! Functions

Number Relationships Science as Inquiry Algebra Origin/Evol. of Univ. How Big is That Math 6-8 Patterns & Technology Star? Functions Design/Understanding Statistics

Adv Alg 9-12 Pattern Recognition Origin/Evol. of Univ. Stars and Slopes

Struct./Prop. of Matter Supernova Chemistry 11-12 Pattern Recognition Origin/Evol.of Univ. Chemistry!

http://imagine.gsfc.nasa.gov/docs/teachers/lesson_plans.html (1 of 2) [5/26/1999 11:38:31 AM] Imagine the Universe! Lesson Plans

Detective Digit Technology and the Slap Math 6-9 Statistics Design/Understanding Happy Computer Caper

Algebra Science as Inquiry Statistics Earth and Space Science Math/Sp Sci 6-10 Get The Picture! Discrete Science and Technology Mathematics History and Nature of Science

Number Science as Inquiry Lotto or Life: Relationships Origin/Evol. of Univ. Math/Sp Sci 6-9 What Are the Patterns & Technology Chances? Functions Design/Understanding

Our lesson plans are being developed by both teachers and the Imagine the Universe! Team. If you have an idea you'd like to contribute, be sure to write us at [email protected].

Ask a Other The Imagine! Imagine! Imagine Satellites Teachers NASA Good Imagine Homepage Feedback Science! & Data Corner Scientist Resources Dictionary

http://imagine.gsfc.nasa.gov/docs/teachers/lesson_plans.html (2 of 2) [5/26/1999 11:38:31 AM] Other Resources (A-G) Other Resources (A-G)

H - R S - Z

ACTIVE GALACTIC NUCLEI ● http://starchild.gsfc.nasa.gov/docs/StarChild/universe_level1/quasars.html This page contains information on quasars for the K-4 student, with a question at the end and links to a glossary of defined terms. ● http://starchild.gsfc.nasa.gov/docs/StarChild/universe_level2/quasars.html This page contains information on quasars written for the 5-8 grade student, with a question at the end and words linked to a glossary of terms.

Books

● Gaustad, John & Zeilik, Michael, Astronomy: The Cosmic Perspective- second edition, John Wiley & Sons, Inc., 1990. This text was designed for an introductory astronomy course for upper high school or undergraduate students who want a comprehensive view and understanding of modern astronomy, including active galaxies (see chapter26). ● Giacconi, R. & Tucker, W., The X-ray Universe, Harvard University Press, 1985. Considered to be another 'classic' X-ray astronomy text book. Includes discussion of active galaxies (see Chapter 13) at a level intended for the undergraduate science major, or above. ● Kaufmann, William J. III, Universe, Freeman and Company, 1994. This book comes highly recommended from both students and scientists. It explains many concepts in astronomy from cosmology to high-energy astrophysics, including information on active galaxies (see Chapter 27). Intended for the upper high school student with a strong science background and interest, or the undergraduate science major taking a basic astronomy course. ● Mitton, Jacqueline & Simon, The Young Oxford Book of Astronomy, Oxford University Press, Inc., 1995. This book explains many concepts in astronomy from the Solar System, galaxies and the Universe, including active galaxies. Intended for the middle or high school student. ● Seward, Frederick D. and Charles, Philip A., Exploring the X-ray Universe, Cambridge University Press, 1995. Explains X-ray astronomy and astrophysics along with its most recent developments. Intended for the undergraduate science major, or above.

Magazine Articles

● Bland-Hawthorne, Jonathan & Cecil, Gerald & Veilleux, Sylvain, "Colossa Galactic Explosions", Scientific American, February 1996, vol. 274, no. 2. Explains the formation and characteristics of active galaxies. Intended for the high school student interested in science, or above. ● Clarke, Stuart, "Mystery at the Heart of Active Galaxies", Astronomy Now, February 1995, vol. 9,

http://imagine.gsfc.nasa.gov/docs/resources/resources_a.html (1 of 9) [5/26/1999 11:38:47 AM] Other Resources (A-G) no. 2. Examines whether the many types of active galaxies (quasars, radio galaxies, and Seyferts), are all the same type of object but viewed from different angles. Intended for the high school student interested in science, or above. **************************************************************

ASTRONOMY See GENERAL ASTRONOMY. **************************************************************

BINARY STAR SYSTEMS ● http://www.isc.tamu.edu/~astro/binstar.html This Web site contains much information and other links related to binary star systems. It is maintained by Dan Bruton of the Department of Physics and Astronomy at Stephen F. Austin State University. For students in high school and above. ● http://www.gettysburg.edu/project/physics/clea/CLEAdesc.html This lab, 'Binary Star Light Curves', was produced by Project CLEA and examines how to determine the period of a variable star from irregularly sampled measurements of its brightness. The CLEA Project is associated with Gettysburg College, and develops laboratory exercises which illustrate modern astronomical techniques using digital data and color images. They are suitable for high school and college classes at all levels, but come with defaults set for use in introductory astronomy classes for non-science majors.

Books

● Gaustad, John & Zeilik, Michael, Astronomy: The Cosmic Perspective- second edition, John Wiley & Sons, Inc., 1990. This text was designed for an introductory astronomy course for upper high school or undergraduate students who want a comprehensive view and understanding of modern astronomy, including binary stars (see Chapter 17). ● Giacconi, R. & Gursky, H., X-Ray Astronomy, D. Reidel Publishing Company. Known as a 'classic' X-ray astromomy text book. Includes discussion of binary stars (see Chapters 1 & 4) at a level intended for the undergraduate science major, or above. ● Giacconi, R. & Tucker, W., The X-ray Universe, Harvard University Press, 1985. Considered to be another 'classic' X-ray astromomy text book. Includes discussion of binary stars (see Chapter 6) at a level intended for the undergraduate science major, or above. ● Kaufmann, William J. III, Universe, Freeman and Company, 1994. This book comes highly recommended from both students and scientists. It explains many concepts in astronomy from cosmology to high-energy astrophysics, including information on binary stars (see Chapter 18). Intended for the upper high school student with a strong science background and interest, or the undergraduate science major taking a basic astronomy course.

http://imagine.gsfc.nasa.gov/docs/resources/resources_a.html (2 of 9) [5/26/1999 11:38:47 AM] Other Resources (A-G) ● Mitton, Jacqueline & Simon, The Young Oxford Book of Astronomy, Oxford University Press, Inc., 1995. This book explains many concepts in astronomy from the Solar System, galaxies, and the Universe, including binary stars. Intended for the middle or high school student. ● Seward, Frederick D. and Charles, Philip A., Exploring the X-ray Universe, Cambridge University Press, 1995. Explains X-ray astronomy and astrophysics along with its most recent developments. Intended for the undergraduate science major, or above. **************************************************************

BLACK HOLES ● http://starchild.gsfc.nasa.gov/docs/StarChild/universe_level1/black_holes.html This page explains for the K-4 student what black holes are and how we know they exist. ● http://starchild.gsfc.nasa.gov/docs/StarChild/universe_level2/black_holes.html This page contains information about black holes and how we know they exist, links to glossary terms and a movie about a "Journey into a Blackhole." ● http://jean-luc.ncsa.uiuc.edu/Movies/ This Web site has virtual reality and informational movies on black holes. This site is associated with NCSA, and is for students in middle school and above.

Books

● Gaustad, John & Zeilik, Michael, Astronomy: The Cosmic Perspective- second edition, John Wiley & Sons, Inc., 1990. This text was designed for an introductory astronomy course for upper high school or undergraduate students who want a comprehensive view and understanding of modern astronomy, including black holes (see Chapters 20 & 21). ● Giacconi, R. & Gursky, H., X-Ray Astronomy, D. Reidel Publishing Company. Known as a 'classic' X-ray astromomy text book. Includes discussion of black holes (see Chapters 4 & 6) at a level intended for the undergraduate science major, or above. ● Giacconi, R. & Tucker, W., The X-ray Universe, Harvard University Press, 1985. Considered to be another 'classic' X-ray astromomy text book. Includes discussion of black holes (see Chapter 7) at a level intended for the undergraduate science major, or above. ● Kaufmann, William J. III, Universe, Freeman and Company, 1994. This book comes highly recommended from both students and scientists. It explains many concepts in astronomy from cosmology to high-energy astrophysics, including information on black holes (see Chapter 24). Intended for the upper high school student with a strong science background and interest, or the undergraduate science major taking a basic astronomy course. ● Levy, David H., A Nature Company Guide: Skywatching, Time-Life Books, 1995. This book provides a general overview and discussion of astronomical objects, including black holes. For students in middle school or above. ● Mitton, Jacqueline & Simon, The Young Oxford Book of Astronomy, Oxford University Press, Inc., 1995. This book explains many concepts in astronomy from the Solar System, galaxies, and the

http://imagine.gsfc.nasa.gov/docs/resources/resources_a.html (3 of 9) [5/26/1999 11:38:47 AM] Other Resources (A-G) Universe, including black holes. Intended for the middle or high school student. ● Rosen, Sidney, How Far is a Star?, Carolrhoda Books, Inc.,1992. With cartoon characters leading the way, you'll find out about our Sun and other stars (including black holes) in this question-and-answer book. Intended for students in elementary school. ● Seward, Frederick D. and Charles, Philip A., Exploring the X-ray Universe, Cambridge University Press, 1995. Explains X-ray astronomy and astrophysics along with its most recent developments. Intended for the undergraduate science major, or above. ● Voyage Through the Universe: Stars, Time-Life Books. This volume is one of a series that examines the Universe in all its aspects. General information for the upper high school student (and above), related to black holes, will be found in the 'Neutron Stars and Black Holes' chapter.

Magazine Articles

● Charles, Philip A. & Wagner, R. Mark, "Black Holes in Binary Stars: Weighing the Evidence", Sky and Telescope, May 1996, vol. 91, no. 5. >From this article, one can understand that by making X-ray observations, astronomers are sometimes able to detect black holes (especially when coupled to a normal star in a binary system). Intended for the high school student interested in science, or above. ● Schulkin, Bonnie, "Does a Monster Lurk Closeby", Astronomy, September 1997, vol. 25, no. 9. Describes the possibility of a massive black hole existing at the heart of our Milky Way Galaxy. Intended for the high school student interested in science, or above. ● Berstein, Jeremy, "The Reluctant Father of Black Holes", Scientific American, June 1996, vol. 274, no. 6. Discusses the details of how Einstein's equations of gravity are the foundation of the modern view of black holes. Intended for the high school student who is interested in science, and above. **************************************************************

CATACLYSMIC VARIABLES ● http://www.kusastro.kyoto-u.ac.jp/vsnet/index.html This Web site contains basic information on CVs, at a level appropriate for high school students and their teachers. Also included are links to research sites, conference notices, etc. ● http://sousun1.phys.soton.ac.uk/~trm/cv_picture.html This Web site gives a nice description along with some model diagrams of CV system evolution. Might be useful to an advanced high school student, but clearly aimed at a college level.

Magazine Articles

● "Accretion Disks in Interacting Binary Stars" by Canizzo & Kaitchuck, 1992, Scientific American, January, 92-99. ● "Henry Norris Russel Prize Lecture of the American Astronomical Society: Fifty years of novae" by Payne-Gaposchkin, 1977, AJ 82, 665-673. Even though this appeared in a professional journal, it is appropriate for serious amateur astronomers and undergraduates majoring in physical sciences.

http://imagine.gsfc.nasa.gov/docs/resources/resources_a.html (4 of 9) [5/26/1999 11:38:47 AM] Other Resources (A-G) **************************************************************

COMETS

Books

● Rosen, Sidney, Can You Hitch a Ride on a Comet?, Carolrhoda Books, Inc.,1992. With cartoon characters leading the way, you'll find out all kinds of information about comets in this question-and-answer book. Intended for students in elementary school. **************************************************************

COSMIC RAYS ● http://helios.gsfc.nasa.gov Produced by the ACE project at NASA Goddard Space Flight Center, this site is designed to increase interest in cosmic rays and heliospheric science. (The heliosphere is the HUGE area in space affected by the Sun.) It also includes some astrophysics basics, a glossary, a history of cosmic ray studies, and the chance to "Ask a Physicist." High school level or above. **************************************************************

DARK MATTER ● http://heasarc.gsfc.nasa.gov/Images/rosat/display/darkmatter.html This is a display from ROSAT. It has some information about dark matter in a short paragraph as well as data from the satellite. It is a good resource for middle/high school students and teachers. ● http://physics7.berkeley.edu/darkmat/dm.html This is a basic description of what dark matter is, why we think it exists, and why it is important for cosmology. It contains a lot of text, but is understandable and defines the terms that are used. Links to more information (including books!) are given at the end. Appropriate for high school/undergraduate physics students. ● http://web.mit.edu/afs/athena.mit.edu/user/r/e/redingtn/www/netadv/dkmatter/gen.html This is a list of links to dark matter pages. The list is divided into sections based on the difficulty level of the referenced sites. ● http://web.mit.edu/afs/athena.mit.edu/user/r/e/redingtn/www/netadv/dkmatter.html This is the basic description page that goes along with the links above. It is accessible to high school/undergraduates. ● http://physics7.berkeley.edu/darkmat/essay.html This is an essay on dark matter including its effects at different size scales, evidence for and against

http://imagine.gsfc.nasa.gov/docs/resources/resources_a.html (5 of 9) [5/26/1999 11:38:47 AM] Other Resources (A-G) it, how much we expect there to be, etc. VERY LONG, but very thorough. ● http://pilot.msu.edu/user/vanhoose/astro/0023.html HST results (1994) showing that red dwarfs do not make up the bulk of the dark matter. This reads like a NASA press report,but anyone who can read a newspaper would get something out of this article. Has background information, too. ● http://zebu.uoregon.edu/text/darkmatter.txt This is "text only". Covers important points and also fairly recent discoveries which contribute to our understanding of dark matter. Accessible for high school.

Magazine Articles

● "Dark Matter and the Origin of Cosmic Structure", Sky and Telescope. October 1994. Good resource for high school aged students and teachers. Back issues are $4.50 within the USA. Instructions on how to order can be found at: http://www.skypub.com/s_t/s_tback.html#order. ● "Searching for Dark Matter", Sky and Telescope. January 1994. High school.

Books

● "Invisible Matter and the Fate of the Universe", by Barry Parker; a decent non-technical book on dark matter, although a little dated (1989) **************************************************************

DIFFUSE BACKGROUND ● http://lheawww.gsfc.nasa.gov/users/snowden/shadow/shadow.html This site contains historical background, current models, pictures, and relevant papers on soft X-ray diffuse background. It is associated with the Laboratory for High Energy Astrophysics, and is intended for college level science majors.

Books

● Giacconi, R. & Gursky, H., X-Ray Astronomy, D. Reidel Publishing Company. Known as a 'classic' X-ray astromomy text book. Includes discussion of diffuse background (see Chapter 10) at a level intended for the undergraduate science major, or above. ● Giacconi, R. & Tucker, W., The X-ray Universe, Harvard University Press, 1985. Considered to be another 'classic' X-ray astromomy text book. Includes discussion of diffuse background (see Chapter 15) at a level intended for the undergraduate science major, or above. ● Seward, Frederick D. and Charles, Philip A., Exploring the X-ray Universe, Cambridge University Press, 1995. Explains X-ray astronomy and astrophysics along with its most recent developments. Intended for the undergraduate science major, or above.

http://imagine.gsfc.nasa.gov/docs/resources/resources_a.html (6 of 9) [5/26/1999 11:38:47 AM] Other Resources (A-G) **************************************************************

EARTH ● http://www.globe.gov/ Global Learning and Observations to Benefit the Environment (GLOBE) is a worldwide network of students, teachers, and scientists working together to study and understand the global environment. **************************************************************

GALAXIES

Books

● Rosen, Sidney, Which Way to the Milkyway?, Carolrhoda Books, Inc.,1992. With cartoon characters leading the way, you'll find out much about our Milky Way and other galaxies in this question-and-answer book. Intended for students in elementary school. **************************************************************

GAMMA RAY BURSTS ● http://www.astro.ucla.edu/irlab/grb.htm This is a thorough history and description of the current theory of gamma-ray bursters. Good general information presented at a level appropriate for high school students. ● http://www.lucifer.com/if-lists/if-sci/0035.html This is a detailed explanation of the reasoning and evidence for belief that gamma-ray bursters are not limited to the Milky Way. A good jumping off point for reports and such for high school students.

Magazine Articles

● "Unsolved Mysteries of the Sun -- Part II; Gamma-Ray Bursts: A Growing Enigma" Sky and Telescope. September 1996. Aimed at the mature astronomer and a good resource for high school aged students and teachers. ● "A New View to a Kill", by Peter Kurczynski. Mercury Magazine. Volume 27, #4. July/August 1997. For the first time since gamma-ray bursts were discovered, these elusive high-energy flashes have shown up in X-ray and optical images. Written for the motivated non-expert. Appropriate for high school/undergraduates. ● "The Mother of All Fireworks", by Peter Kurczynski. Mercury Magazine. Volume 25 #5. September/October 1996. Spy satellites saw them first. They blast with the energy of a supernova. And every time astronomers think they know what they are, gamma-ray bursts reveal a surprise. ● Fishman, Gerald J. & Harmann, Dieter H., "Gamma-Ray Bursts", Scientific American, January

http://imagine.gsfc.nasa.gov/docs/resources/resources_a.html (7 of 9) [5/26/1999 11:38:47 AM] Other Resources (A-G) 1997, vol. 277, no. 1. Explains one of the most powerful explosions in the Universe. Intended for the high school student interested in science, or above. **************************************************************

GAMMA-RAY DETECTORS ● http://cossc.gsfc.nasa.gov/ This Web site is the Compton Gamma-Ray Astronomy home page. It has a lot of information presented in a fairly straightforward way. Includes images, new discoveries, and specs on the instruments. Unfortunately information on many levels is all mixed in together, from middle school to college. **************************************************************

GENERAL ASTRONOMY ● http://starchild.gsfc.nasa.gov The Imagine the Universe! counterpart for younger astronomers. This site is aimed at students grades K-4 (designated Level 1) and 5-8 (designated Level 2). It contains easy-to-understand information about the solar system, the Universe, and other "space stuff" as well as activities, movies, puzzles, etc. Each topic has a short quiz at the end. This site, written by middle school teachers, is a great educational resource with lots of fun! ● http://cnde.iastate.edu/staff/jtroeger/astronomy.html This Web site is an astronomy course for middle/high school students using the Internet. ● http://heasarc.gsfc.nasa.gov/docs/www_info/webstars.html WebStars: Astrophysics in Cyberspace, a large list of other astronomy sites, with short descriptions. ● http://antwrp.gsfc.nasa.gov/apod/astropix.html Astronomy Picture of the Day: Each day a different image or photograph of our fascinating Universe is featured, along with a brief explanation written by a professional astronomer. Archived pictures (sorted by date and by subject) go back to June, 1995. The text is very informative and contains useful links to related information. Accessible for high school students and above. **************************************************************

Ask a Other The Imagine! Imagine! Imagine Satellites Teachers NASA Good Imagine Homepage Feedback Science! & Data Corner Scientist Resources Dictionary

http://imagine.gsfc.nasa.gov/docs/resources/resources_a.html (8 of 9) [5/26/1999 11:38:47 AM] Other Resources (A-G)

http://imagine.gsfc.nasa.gov/docs/resources/resources_a.html (9 of 9) [5/26/1999 11:38:47 AM] Imagine The Universe!

Welcome to Imagine the Universe!

A service of the High-Energy Astrophysics Learning Center

This site is dedicated to a discussion about our Universe... what we know about it, how it is evolving, and the kinds of objects and phenomena it contains. Just as importantly, we also discuss how scientists know what they know, what mysteries remain, and how they might one day find the answers to these questions. This site is intended primarily for ages 14 and up. If you are interested in a lower level, more basic discussion about astronomy and space exploration, try our StarChild site. It may have just what you are looking for! You will navigate around our site using a series of buttons at the bottom of each page. This is your chance to learn about the navigation buttons!

Any time you see , you can go to a new window showing the Math and Science Education Standards for that page. When you are done viewing the standards, close that window to return to the page you were on previously.

http://imagine.gsfc.nasa.gov/docs/homepage.html (1 of 2) [5/26/1999 11:39:14 AM] Imagine The Universe! Please take our survey!

Special Features of Our Site! Search Our Site for Your Topic!

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http://imagine.gsfc.nasa.gov/docs/homepage.html (2 of 2) [5/26/1999 11:39:14 AM] The Imagine the Universe! Post Office The Imagine the Universe! Post Office

IMPORTANT! This email address IS NOT TO BE USED TO SUBMIT SCIENCE QUESTIONS FOR A RESPONSE. Any such questions submitted to this address will not be forwarded to our service which answers such questions. If you have a science question, visit Ask a NASA Scientist. Your email address:

Subject:

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You must provide your correct, complete e-mail address in order for us to respond to you. For example, [email protected] or [email protected] or [email protected].

http://imagine.gsfc.nasa.gov/cgi-bin/feedback_button.pl [5/26/1999 11:39:16 AM] Ask a NASA Scientist

Ask a NASA Scientist!

Lots of people have all sorts of questions about things such as black holes, quasars, dark matter, and so much more. But they don't ask because they don't know who to ask or don't want to look silly or aren't sure how to ask. Now you can ask a question about our science from the privacy of your own computer!

But wait - here are some things you need to know! Younger readers (ages 4-14) may find the information they need about general astronomy and spaceflight on StarChild. We receive hundreds of questions every month. We cannot answer all the questions we receive. We've already answered lots of questions - maybe we've answered yours! Before asking your question, please browse through our ARCHIVE OF PREVIOUSLY ANSWERED QUESTIONS ● If you don't have the time to read through our archive, try our ARCHIVE SEARCH ENGINE. ● How do I seach the Web effectively? ● Who are we and what kind of questions do we specialize in? - We are not the real expert you may be looking for, on Human Space Flight or the Solar System. Interested in backyard astronomy or amateur astronomy? ● We are now asking you to submit no more than 1 question per week. ● Teachers, please see Special Guidelines for Teachers.

http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html (1 of 3) [5/26/1999 11:39:21 AM] Ask a NASA Scientist Hot Topic

● Information on the newly discovered solar system (Upsilon Andromedae)

Other hot topics and recently answered questions.

Special Features These are longer explanations that try to answer many questions that we have received on the same (or related) topic. ● Are we going to be hit by an asteroid? ● The Cosmic Distance Scale

Primary Areas of Interest and Expertise:

Astronomy as a Profession Neutron stars Binary Star Systems Quasars Black Holes Relativity Cosmology Stars Dark Matter Supernovae and Their Remnants Galaxies X-rays and Gamma-rays

We also answer questions in other categories.

● Submit Your Question

It usually takes 1-3 weeks for our volunteers to answer a question. If we are especially busy, it may take longer.

http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html (2 of 3) [5/26/1999 11:39:21 AM] Ask a NASA Scientist Ask a Other The Imagine! Imagine! Imagine Satellites Teachers NASA Good Imagine Homepage Feedback Science! & Data Corner Scientist Resources Dictionary

http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html (3 of 3) [5/26/1999 11:39:21 AM] Science Links

Imagine the Science! The Science Section of Imagine the Universe!

Here you can find all sorts of information related to what we know about the structures in, and the evolution of, our Universe. There is information about how we know what we know, what mysteries still remain, and how scientists hope to discover the answers to some of these puzzles. The Universe we explore here is the Universe of pulsars, black holes, supernovae, gamma-ray bursts, dark matter, and quasars. It is a Universe of extremes -- extremely high energies, extremely high densities, extremely high pressures, extremely intense magnetic fields. It is a Universe we can use as the ultimate laboratory, achieving physical conditions which we cannot replicate here on Earth, which allow us to test our understanding and application the laws of physics. It is an amazing Universe, just Imagine! Imagine What We Know

Active Galaxies & Quasars Binary Systems Black Holes Cataclysmic Variables Dark Matter Diffuse Background The Electromagnetic Spectrum Gamma-Ray Astronomy Gamma-Ray Bursts Multiwavelength Astronomy Pulsars Stars The Sun Supernovae White Dwarfs X-ray Astronomy X-ray Transients

http://imagine.gsfc.nasa.gov/docs/science/science.html (1 of 2) [5/26/1999 11:39:27 AM] Science Links Imagine How We Know It

Gamma-Ray Generation Gamma-Ray Telescopes & Detectors Lightcurves, Spectra, and Images Spectral Analysis Timing Analysis X-ray Detectors X-ray Generation X-ray Telescopes

Imagine the Remaining Mysteries

Origin and Destiny of the The Lumpy Universe Evolution of Known Structures Universe Growth of Massive Black Development of Elements in the Evolution of Galaxies Holes Universe Matter in Extreme Conditions Validation of Relativity Nature of Dark Matter

Imagine Finding the Answers

Higher Resolution Greater Collection Area Exploring New Wavelengths

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http://imagine.gsfc.nasa.gov/docs/science/science.html (2 of 2) [5/26/1999 11:39:27 AM] Satellites, Data, and Software Satellites and Data

Welcome to an Introduction to Satellites and their Data. Here you can find out all about the satellites, their missions, the kinds of data they produced, and the exciting discoveries derived from those data. The Satellites

Probing the structure and evolution of our Universe and the objects its contains requires, in general, that we make our observations above Earth's absorbing atmosphere. Starting with sounding rocket flights in the late 1940s, scientists have been able to develop ever-better instruments to probe deeper into space and finer into the details of our cosmos. This section will allow you to learn about the satellites and missions which have provided scientists the foundation of "what we know".

Tell Me about X-ray Astronomy Satellites & Missions Tell Me about Gamma-ray Astronomy Satellites & Missions Tell Me about Cosmic Ray Satellites & Missions The Data

The information, or data, about our Universe measured by the instruments aboard satellites are transferred to the ground and analyzed by scientists. The data can arrive in many forms and much processing is usually required before it can be used to "do science". This section will discuss the data, the typical processing, the final data archive, the scientific analysis process, and the final scientific results.

Tell Me about Getting Data from the Satellite to the Ground Tell Me about Data Processing Tell Me about Data Archives Tell Me about Data Analysis Tell Me about Scientific Results from Data

Ask a Other The Imagine! Imagine! Imagine Satellites Teachers NASA Good Imagine Homepage Feedback Science! & Data Corner Scientist Resources Dictionary

http://imagine.gsfc.nasa.gov/docs/sats_n_data/sats_n_data.html (1 of 2) [5/26/1999 11:39:30 AM] Satellites, Data, and Software Imagine the Universe! is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Nicholas E. White (Director), within the Laboratory for High Energy Astrophysics (LHEA) at NASA/ GSFC. Website Text Authors: The Imagine! Team Project Leader: Dr. Laura Whitlock Technical Rep: Sherri Calvo Comments or Feedback about our site can be sent to: [email protected]. Science-related questions should be directed to Ask a NASA Scientist .

http://imagine.gsfc.nasa.gov/docs/sats_n_data/sats_n_data.html (2 of 2) [5/26/1999 11:39:30 AM] Other Good Resources

Pathways to Astronomy Education Resources

The Universe is a very big place...and there are many ways to explore it. In this Section of Imagine the Universe!, we will provide you with the pathways to other World-Wide Web sites, posters, books, magazines, slide sets, movies, and whatever else we could find that we think you'll find useful. Show me the topics:

[A - G] [H - R] [S - Z]

Active Galactic Nuclei Astronomy Stars Binary Star Systems Stellar Coronae Black Holes History of Gamma-ray Astronomy Sun Cataclysmic Variables History of X-ray Astronomy SN And Their Remnants Comets Infrared Ultraviolet Cosmic Rays Multiwavelength Astronomy Visible Dark Matter Neutron Stars White Dwarfs Diffuse Background Pulsars X-ray Astronomy Earth Quasars X-ray Binaries Galaxies Radio X-ray Telescopes And Detectors Gamma-ray Bursts X-ray Transients Gamma-ray Detectors General Astronomy

http://imagine.gsfc.nasa.gov/docs/resources/pathways.html (1 of 2) [5/26/1999 11:39:40 AM] Other Good Resources

Ask a Other The Imagine! Imagine! Imagine Satellites Teachers NASA Good Imagine Homepage Feedback Science! & Data Corner Scientist Resources Dictionary

Comments or Feedback about our site can be sent to: [email protected]. Science-related questions should be directed to Ask a NASA Scientist .

http://imagine.gsfc.nasa.gov/docs/resources/pathways.html (2 of 2) [5/26/1999 11:39:40 AM] The Teacher's Corner: Multidisciplinary Classroom Activities

The Teacher's Corner

Want to "Know What our Long-Term Plans Are and Where You Might See Us?"

Currently, our Teacher Resources include: Lesson Plans Adopt an Astronomer Information about NASA education initiatives and opportunities Other Education Resources about Imagine the Universe! topics Other Good General Science Education Web Sites Life Cycles of Stars - Information and Activity Booklets The Anatomy of Black Holes - Information and Activity Booklets

Send us your comments to [email protected]

http://imagine.gsfc.nasa.gov/docs/teachers/teachers_corner.html (1 of 2) [5/26/1999 11:39:46 AM] The Teacher's Corner: Multidisciplinary Classroom Activities Ask a Other The Imagine! Imagine! Imagine Satellites Teachers NASA Good Imagine Homepage Feedback Science! & Data Corner Scientist Resources Dictionary

http://imagine.gsfc.nasa.gov/docs/teachers/teachers_corner.html (2 of 2) [5/26/1999 11:39:46 AM] HEASARC/GSFC Home Page X-Ray Astronomy Program Working Group

[HEASARC Information] [Archive] [Software] [Calibration] [What's New] [Links] [Public Outreach & Education] [Missions] [ASCA] [BeppoSAX] [CGRO] [ROSAT] [RXTE] [EUVE] [Astro-E] [AXAF] [Integral] [XMM] [Spectrum-X-Gamma]

http://heasarc.gsfc.nasa.gov/ (1 of 2) [5/26/1999 11:40:15 AM] HEASARC/GSFC Home Page

You are visitor number 397842. This file was last modified on Tuesday, 22-Dec-1998 14:51:28 EST

Part of the NASA OSS Structure and Evolution of the Universe theme. A service of the Laboratory for High Energy Astrophysics (LHEA) at NASA/ GSFC HEASARC Director: Dr. Nicholas E. White, [email protected] Technical Rep: Sherri Calvo, [email protected] Questions/Comments/Feedback NASA's Privacy Statement Tell me about black holes, astronomy, and more!

http://heasarc.gsfc.nasa.gov/ (2 of 2) [5/26/1999 11:40:15 AM] Dr. Nicholas White

Dr. Nicholas White - HEASARC Director

● Office: GSFC Building 2, 250 ● Address: Code 662, GSFC, Greenbelt, MD, 20771, USA ● Phone: 301 286 8443 ● Fax: 301 286 1684 ● e-mail: [email protected] ● Home Page (Papers, publications and pictures) ● Curriculum Vitae

A Message from the Director

Following recommendations from the NASA advisory committees, the HEASARC was established in 1990 to archive the data from X-ray and Gamma-ray astronomy missions including the ASCA, Compton

http://heasarc.gsfc.nasa.gov/docs/bios/white.html (1 of 2) [5/26/1999 11:40:39 AM] Dr. Nicholas White GRO, ROSAT, XTE , EUVE and BeppoSAX observatories. HEASARC is also responsible for restoring datasets from historic missions flown since the field of X-ray and Gamma-ray astronomy began in the 1960s. We retain and distribute not only all of the data from NASAs high energy astrophysics missions, but also that from European and Japanese satellites. Currently the HEASARC data holding total over 1 Terrabyte of data, with all of these data available for immediate ftp download via our W3Browse and Skyview user interfaces. The HEASARC is currently one of the largest online astronomy archives. But the HEASARC is more than just an archive for X-ray and Gamma-ray astronomy data. To effectively use these multi-mission data it is important to provide a mission independent infrastructure for their access and analysis. To do this the HEASARC has pioneered the setting of software and data format standards across many different missions. This multimission approach both saves money through the reuse of software and promotes a multi-mission/multi-wavelength approach to the data analysis. As we look forward to the major X-ray and Gamma-ray observatories Chandra Observatory, XMM, Astro-E and Integral to be launched around the turn of the century, the infrastructure laid down by the HEASARC provides a sound basis for the future. Over the coming years we plan to build on the current infrastructure to provide more value-added interfaces to the archive, that will provide on demand higher level products in the most usefull form required. As Director of the HEASARC I am responsible for all aspects of the HEASARC operations. I welcome and encourage comments (both positive and negative) from our community of users. The HEASARC Users Group (HUG) meets once per year to give me advice and feedback on the HEASARC activities. I also monitor the Feedback e-mail line and I encourage you to send in comments and suggestions. About the Director

Return to the OGIP Staff page

Page Last Update: Monday, 1-Jun-1999

http://heasarc.gsfc.nasa.gov/docs/bios/white.html (2 of 2) [5/26/1999 11:40:39 AM] NASA's GSFC LHEA

NASA's GSFC ---> Space Sciences'

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part of the Structure and

Evolution of the Universe Theme

Office of Guest Gamma and Cosmic Ray X-ray Instrument Development Investigator Programs: Includes User Support Facilities and the

High Energy Astrophysics Science Archive Research Center

Events Key Personnel Coming/ Recent Past/ Ongoing/ Other Local Seminars and Talks

http://lheawww.gsfc.nasa.gov/docs/lhea/homepg_lhea.html (1 of 2) [5/26/1999 11:40:47 AM] NASA's GSFC LHEA

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Research Areas Programs Graduate Students

Reports and Lists 1998 Annual AAS Report including Publications (in PDF) / Staff Listing

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A service of the Laboratory for High Energy Astrophysics (LHEA) at NASA's GSFC -- Astronomy Questions??? Ask a NASA Scientist. -- NASA specific Questions??? Try the NASA Homepage or start at the NASA site map. -- LHEA Web related Questions and Comments to: webmaster, Eunice Eng, [email protected]

This page was last modified: Friday, 21-May-99 09:53:44.

http://lheawww.gsfc.nasa.gov/docs/lhea/homepg_lhea.html (2 of 2) [5/26/1999 11:40:47 AM] NASA Homepage

May 26, 1999

"NASA is deeply committed to spreading Hubble Measures the unique knowledge that flows from its Expanding Universe aeronautics and space Interested in the latest information NASA has to research...." The Hubble Space offer? Then take a look at Telescope Key Project Read NASA [email protected]. This on-line Administrator Daniel S. Team today announced Goldin's welcome letter, that it has completed newsletter, updated daily, bio and speeches. efforts to measure precise contains the latest news about NASA science and technology. Welcome to NASA Web distances to far-flung galaxies, an essential ■ Hubble Measures Expanding ingredient needed to determine the age, Universe Navigating NASA's size and fate of the universe. "Before ■ NASA Spacecraft Spot Mars Strategic Enterprises Hubble, astronomers could not decide if the Weather System Office of Aero-Space universe was 10 billion or 20 billion years ■ Nobel Prize Winner to Lead Technology old," according to the team leader. "After NASA Astrobiology Institute Human Exploration and all these years, we are finally entering an Development of Space era of precision cosmology. Now we can Earth Science more reliably address the broader picture of Space Science the universe's origin, evolution and destiny." (Full Story) More About NASA: (5/25/99) Doing Business Cool NASA Websites with NASA Educational Resources Freedom of Information Act History Other Cool NASA Websites Jobs and Internships [Frequently Asked Questions] [Hot Topics] [Multimedia Gallery] [NASA Television] [Textonly Version] [NASA Privacy Statement] [Site Map] News and Information Author: Brian Dunbar http://www.nasa.gov/NASA_homepage.html/ (1 of 2) [5/26/1999 11:41:09 AM] NASA Homepage Organization Curator: Sudha V. Chudamani and Subject Comments and Questions Index Last Updated: May 26, 1999 Project Home Pages Research Opportunities Scientific and Technical Information See a Launch Launch Schedule Spinoffs and Commercial Technology Visiting NASA

http://www.nasa.gov/NASA_homepage.html/ (2 of 2) [5/26/1999 11:41:09 AM] NASA Goddard Space Flight Center Homepage Welcome to Goddard Newsroom Organizations Hubble Latest News Public Completes Programs Eight-Year TERRIERS Visitor Center Effort To Satellite Out Of Measure Power; Recovery Education Expanding Team To Be Universe (Details) Formed (Details) Science (Caption) Question Dr. Antonio J. (Animations) of the Week Busalacchi STS-96 - Receives Business Presidential Rank Managers Set May 27 6:32 am EDT. Opportunities As Target Launch Date For Meritorious Discovery (Details) Executive Award FOIA The launch of STS-96 has slipped to (Details) May 27. Crews found over 150 Photo/Movie dents and nicks from hail in the foam insulation on the external tanks. Dr. Vincent V. Gallery STS-96 is a logistics and resupply mission for the International Space Salomonson Station. It will be the first flight to Receives The Library dock to the International Space Station. The SPACEHAB double Presidential FAQ module will carry internal and resupply cargo for station outfitting. Distinguished Other payloads are the Student Rank Award Wallops Tracked Atmospheric Research Satellite for Heuristic International (Details) Flight Facility Networking Equipment (STARSHINE), the Shuttle Vibration Forces Experiment (SVF) Earth Science NASA and the Orbiter Integrated Vehicle Health Monitoring - HEDS Updates Centers Technology Demonstration (IVHM HTD). Earth Sciences and You

http://www.gsfc.nasa.gov/ (1 of 2) [5/26/1999 11:41:18 AM] NASA Goddard Space Flight Center Homepage Intranet 1959--1999Current Events (NASA Only) Goddard is 40 this year. Visit our Anniversary website for details on our 40 year history and some of Goddard's most notable firsts.

Speeches at Goddard's 4Oth Symposium - Administrator Goldin; Dr. Ghassem Asrar, Associate Administrator, Office of Earth Science; Dr. James E Hansen (pdf file of Charts)

Goddard's overall mission falls into three major areas of responsibility:

SPACE SCIENCE TECHNOLOGY EARTH SCIENCE

"NOTICE: This computer has been assigned a U.S. Government Internet Protocol (IP) address whose use is for authorized government purposes. By accessing and using the computer or its systems, you are consenting to system monitoring, including the monitoring of keystrokes. Unauthorized use of, or access to, this computer system may subject you to disciplinary action and criminal prosecution."

We are interested in what you think, so please send us your comments. Curator: Susan R. Capretti Author: Darlene A. Ahalt Design & Graphics: Martin J. Kiely Responsible NASA Official: Janet K. Ruff Last Revised: 26 May 1999

http://www.gsfc.nasa.gov/ (2 of 2) [5/26/1999 11:41:18 AM] The Imagine the Universe! Team The Imagine! Team

Who Writes this Stuff ??

The materials found in the Imagine the Universe! web site were written by a dedicated group of astronomers and programmers who work at NASA's Goddard Space Flight Center. Some members of this jolly group spend their days recovering data from old X-ray and gamma-ray satellites and making it available to the public for use again. Others spend their time helping various astronomers plan and interpret observations obtained with current satellite missions such as ROSAT, ASCA, the Rossi X-ray Timing Explorer, and the Compton Gamma-Ray Observatory. All of these activities entail astronomers and programmers working together to develop sophisticated computer software and databases. In recent years, much of our effort has turned to providing our services on the web. We are happy to expand these services to a broader community of students, teachers, and the general public who wish to know more about the wondrous Universe.

[Left to Right: (seated) Koji Mukai, Steve Fantasia, Gail Rohrbach, Mike Arida, Jesse Allen, Leonard Garcia, Laura Whitlock (standing) Maggie Masetti, Nick White, Pat Tyler, Padi Boyd, Jim Lochner, Allie Cliffe, Meredith Bene, Tess Jaffe, Damian Audley, Karen Smale] Contributors: Laura Whitlock -- Imagine the Universe's numero uno. It was her idea. When not rescuing data from dusty basements, she studies X-ray binaries. She's also mother to the best Dalmatian in the world. Meredith Bene -- Our web master extraordinaire. She's one of the happiest people we know, likely due to all that Joan Baez and Peter, Paul & Mary that she listens to. Jim Lochner -- Responsible for making sure the Ask a NASA Scientist service works and is archived. Jim works on the RXTE mission, when not listening to "Car Talk". Nick White -- Group leader of the X-ray Group and the Office of Guest Investigator Programs. He's in

http://imagine.gsfc.nasa.gov/docs/lcteam.html (1 of 3) [5/26/1999 11:41:25 AM] The Imagine the Universe! Team control, but not necessarily in charge. Karen Smale -- Web page designer and graphic artist, among other talents. She can draw you a map to anywhere and sing you a tune to send you on your way. Pat Tyler -- A web geek if we ever saw one. Expert at digitizing images and putting them on the web. If it's out there, she knows how to get it. Padi Boyd -- Expert in chaos (no wise cracks !) in astronomy. Leader of well-known (at least in these parts) a cappella group. Koji Mukai -- Expert in cataclysmic variables, ASCA, and sometimes X-ray binaries. Can also give you batting averages of the Baltimore Orioles. Steve Fantasia -- Knows more about the ROSAT source catalog than he cares to talk about. Spends his spare time gardening. Care for a fresh tomato? Paul Butterworth -- High-energy fellow who works on low-energy gamma-rays. He has done lots of educational work. Gail Rohrbach -- Aids guest observers for RXTE. Beyond that, it's just too complicated! Maggie Masetti -- After helping us for a couple of summers, Maggie has joined us permanently. She specializes in archiving questions from our ask-an-astronomer service, keeping the RXTE learning center from looking clinical, and anything you care to know about the Simpsons (or Seinfeld, or The X-files). Daryl Macomb -- Working for the Compton Gamma-Ray Observatory Science Support Center, Daryl likes to think of himself as just a humble guy helping good folks use gamma-ray data. Tom Bridgman -- Tom is the OSSE Instrument Specialist for the CGRO Science Support Center. He likes to do research on compact objects, radiation transport, and accretion. Tom is always happy, for some reason! Allie Cliffe -- An aspiring benevolent dictator, Allie is honing her craft with us by bringing the scientists and their science down to Earth. Jeff Silvis -- A physicist turned UV astronomer turned gamma-ray astronomer, Jeff has an avid interest in philosophies and mythologies of many cultures. He'll cook you an Indian meal while relating a quote from Lao Tsu and telling tales of the Nordic gods. Sandy Antunes -- X-ray satellite scheduler by day, game writer by night, Sandy is working to create time from nothing. Mike Arida - Mike helps all the scientists who come to the HEASARC to analyze data from their favorite satellite. He thinks of himself as an average guy, but he is well-known for his snappy way of dressing.

http://imagine.gsfc.nasa.gov/docs/lcteam.html (2 of 3) [5/26/1999 11:41:25 AM] The Imagine the Universe! Team Ask a Other The Imagine! Imagine! Imagine Satellites Teachers NASA Good Imagine Homepage Feedback Science! & Data Corner Scientist Resources Dictionary

http://imagine.gsfc.nasa.gov/docs/lcteam.html (3 of 3) [5/26/1999 11:41:25 AM] Dr. Laura A. Whitlock Dr. Laura A. Whitlock

Job Description: Astrophysicist Office: GSFC Building 2, Rm. W230 Phone: (301) 286-1578 e-mail: [email protected]

Dr. Laura A. Whitlock serves as a research scientist for the Universities Space Research Association in Greenbelt, Maryland. Currently, she is creating, developing, and promoting education and outreach materials, focusing on the field of high-energy astrophysics and how it probes the structure and evolution of our Universe. A project leader for the "Imagine the Universe!" and "StarChild" Web sites, Whitlock also develops and presents workshops about high-energy astronomy and available education resources to educators at state and national education meetings, conducts National Teacher Training Institute (NTTI) workshops, and leads scientist training workshops. Photo of Dr. Whitlock?

Dr. Whitlock received a BS with honors in Physics from Southwestern at Memphis (now Rhodes College), and a PhD in Physics from the University of Florida in Gainesville. Dr. Whitlock has received numerous awards and fellowships including: the Southwestern Scholar Award, 1977-1981; the Graduate Fellowship for Women in Non-Traditional Careers in 1981; Who's Who in American Science and Engineering; the USRA Community Service and Education Outreach Award; NASA/GSFC Group Achievement Award (HEASARC); Global Information Infrastructure (GII) Award semi-finalist for both the Children and Education categories in 1998 ; and the Webby Award winner for Best Education Web Site in 1998. In her spare time, she still tries to do science. These days she is concentrating her efforts on Rossi X-ray Timing Explorer observations of X- ray binary systems. Tell me more about Dr. Whitlock's: Education Present & Previous Employment Awards and Professional Society Memberships Recent Education/Public Outreach Presentations Scheduled Future Presentations Science Conference and Non-refereed Journal Publications

http://imagine.gsfc.nasa.gov/docs/people/whitlock.html (1 of 2) [5/26/1999 11:41:49 AM] Dr. Laura A. Whitlock Refereed Science Journal Publications

http://imagine.gsfc.nasa.gov/docs/people/whitlock.html (2 of 2) [5/26/1999 11:41:49 AM] Sherri Chasin Calvo Sherri Chasin Calvo

Job Description: Computer Scientist Office: GSFC T2 Rm 55 Phone: (301) 286-5668 e-mail: [email protected] Sherri Calvo received her bachelor's degree in Physics from Rutgers University and a master's degree in Computer Applications and Information Systems from New York University. She is currently progressing a course at a time toward an additional degree in Astronomy. After internships at the Sarnoff Laboratory in Princeton and the New York State Legislative Commission on Science and Technology, and professional experience in computer programming, newspaper reporting and editing, Sherri started at Goddard Space Flight Center in 1989. In the Parts Analysis Laboratory of the Office of Flight Assurance, she worked on engineering reports, spacecraft parts testing, data analysis, electron microscopy, and whatever else was needed. In 1990, she joined the Earth Observing System Data and Information System (EOSDIS) project, where she was the System Engineer for the Information Management System element, and participated in bringing the "Version 0" prototype from conceptual to operational stage. Sherri came to the Laboratory for High Energy Astrophysics in October 1994. She is the lead point-of-contact for information technologies and computer support in the Laboratory, and also serves as the Technical Director of the High Energy Astrophysics Science Archive Research Center (HEASARC), overseeing the various HEASARC systems for archiving and accessing astrophysics data. Curriculum Vitae

http://heasarc.gsfc.nasa.gov/docs/bios/sherri.html [5/26/1999 11:41:50 AM]