Astronomy 180 AST-180 (John F. Wettaw College of Biological Sciences)

8/28/08

Astronomy – The study of the Universe. Universe – All objects in it, its properties, and its evolution. Pseudoscience – Seems like a science, but is not actually a science. Astronomy is the earliest /oldest science.

Reasons for studying Astronomy:

 Fun  Religious  Navigation  Calendar  Curiosity  Astrology  Mythology  Disaster Warning/Prevention  Resources/Expansion  Aid to other sciences  Tides

Scientific Method

1. Make an observation. 2. Make a model (hypothesis). Explain observation Predict future results 3. Test model in a variety of situations. 4. Theory (-> Law potentially)

9/2/08

Patterns of Stars – Constellations (Currently accepted constellations are from the Greeks). They can represent objects, animals, or mythological beings. International Astronomical Union (IAU) – Subdivided the sky info 88 constellations. Angular Measurement – 360 Degrees in a circle, 60 arcminutes in a degree, 60 arcseconds in an arcminute. The full moon or sun are about 0.5 degrees.

Distances in Astronomy:

Within Solar System:

Astronomical Unit (Au) – Average distance between the Earth and the Sun. 1 Au = 93m miles = 9.3 x 107 mi = 1.5 x 108 km

Outside Solar System:

Light year – Distance light can travel in one year. 1 LY = 6 x 1012 mi = 1013 km Parsec – A larger unit of distance. 1 Pa = 3.09 x 1013 = 3.26 LY

Electromagnetic Radiation

 Visible Light  Radio Waves  X-Rays

9/4/08

Asterisms – Prominent groupings of stars not officially recognized as constellations by the IAU. For instance: The Big/Little Dipper, or The Summer Triangle Celestial Sphere – Sphere around earth for computing a stars position. Polaris – The North Star. Circum Polar Stars – Starts that never rise or set. Ecliptic – The Suns path across the Celestial Sphere. Zodiac Constellations – Constellations through which the Sun passes. Declination – The Celestial Sphere’s equivalent of Latitude (N/S). N/S of Celestial Equator. Right Ascension – The Celestial Sphere’s equivalent of Longitude (E/W) 0 RA = The Vernal Equinox Only measured toward the east. Measured in time units (H/M/S). Revolution – The orbital motion of one body around another. Rotation – The spin motion of a body.

Coordinate System (Earth)

Latitude (N-S) 0° Lat = Equator +90° Lat = North Pole -90° Lat = South Pole

Longitude (E-W) 180° W - 180° E 0° Long = Prime Meridian (Greenwich England)

1 Rotation of the earth = 1 day 1 Revolution of the moon around the earth = 1 month 1 Revolution of the earth around the sun = 1 year

9/9/08

Noon-noon – Solar Day, 24hrs. Sidereal Day – Time for stars to return to the same position, 23h 56m 4s. Perihelion – Closest point to the Sun. Aphelion – Farthest point from the Sun. Season – Tilt of rotational axis. Precession – Wobbling of Earth’s rotation axis. Sidereal Month – Time to return to the same background of stars (27 1/3 earth days long). Synodic Month – Time to return to the same phase (29 ½ earth days long).

The Earth’s orbital motion around the sun accounts for 4min difference.

1 Orbit (Revolution) of the Earth around the Sun is 1 Year (365.2425 days).

1 Revolution of the Moon around the Earth is 1 Month.

Earth’s Orbit around the Sun

 Perihelion = 1.47 x 108 – January 4th.  Aphelion = 1.52 x 108 – July 4th.

Sun/Stars create their own energy.

Planets/Moons reflect light.

Phases of the Moon as viewed from above the north pole.

Phases of the Moon as viewed from the earth.

Autumnal Equinox – Sept 21st. Sun overhead at noon at the equator. Equal number of day and night hours. Vernal Equinox – Mar 21st. Sun overhead at noon at equator. Equal number of day and night hours. Summer Solstice – Jun 21st. Sun overhead at noon at 23.5° N Latitude. Max number of daylight hours. Winter Solstice – Dec 21st. Sun overhead at noon at 23.5° S Latitude. Max number of nighttime hours.

9/11/08

Perigee – Moon’s closest approach to Earth. Apogee – When the Moon is farthest from Earth.

Eclipses Solar Eclipse – Moon blocks out light from sun as seen from Earth. New Moon phase only. Total Solar Eclipse – Occurs when the Moon completely blocks out the sun. Annular Solar Eclipse – Occurs when the Moon is near apogee. Lunar Eclipse – Moon moves into the Earth’s shadow.

History of Astronomy

Greeks Earth is the center of the Universe (Geocentric Model). Parallax – Point of view changes how you see things (Stellar Parallax). Proves either: A) Earth is stationary - OR - B) Stars are VERY far away.

Circular Orbits Direct Motion – W -> E Motion Retrograde Motion – Backwards (E -> W) Motion

Ptolemy – Came up with Epicycle model.

1500’s Nicolas Copernicus Heliocentric Model (Sun Centered) – Earth orbits the Sun with other planets.

Planetary Configurations Inferior Planets –Lie between the Sun and Earth. Superior Planets – Lie beyond the Earth’s Orbit.

9/16/08

Planetary Configurations Superior Planets

Tycho Brahe 1572 – Supernova 1563 – Jupiter/Saturn come close Accurate observations of planetary positions

Johannes Kepler Eliptical Orbits

Kepler’s Laws of Planetary Motion

Law 1: Laws of Ellipses – Planets move in elliptical orbits around sun with the sun at one focus.

Law 2: Law of Equal Areas – A line joining the planet and the sun sweeps out equal areas in equal amounts of time.

Planets move faster when when near Perhelion then when near Aphelion.

Law 3: Harmonic Law – The cube of a planet’s semimajor axis (a) is related to the square of its orbital period (p). P2=Ka3 P in earth years, a in Au then K=1. Mars: Orbital Period = 2 yrs = 4 = a = 3√4 = 1.51

9/18/08

Galileo Galilei

1609

1. Moon is not smooth 2. Sun has spots 3. Milky Way – stars 4. Venus goes through phases 5. Saturn has bulges (turns out to be rings) 6. Jupiter has moons

Book: Dialogue on the two great world systems. 3 men arguing: Geocentric Model (Simplicio), Heliocentric Model, Undecided.

Isaac Newton

Laws of Motion: 1. Inertial Law – A body at rest or one in motion at constant speed with remain in that state unless acted on by a outside force. 2. Force Law – The force is equal to the mass of the object times its acceleration (F=ma). 3. Reaction Law – For every act there is a equal and opposite reaction.

Law of Gravitation The attractive force between two objects is proportional to the product of their masses and inversely proportional to the square of the distance between them. G = Universal Gravitational Constant

Centripetal Velocity

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Escape Velocity – How fast you have to move to escape a gravitational field.

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Light

Electromagnetic Radiation Wave Length Nanometer – 10-9 m Frequency – Number of crests per unit of time Hertz (Hz) = Number/Sec λf = Velocity of wave = Speed of Light (in a vacuum 3 x 105 km/s)

Wave-Particle Duality Particle = Energy Packet = Photon E = Constant/λ Telescope Reflection Oi = Angle of Incidence Or = Angle of Reflection Oi = Or

Refraction (Bend Light) Oi = Angle of Incidence Ot = Angle of Transmission Oi ≠Ot

V1 = SOL in Air

V2 = SOL in Glass V1 > V2 Ot < Oi

9/23/08

Convex Lens

Refracting Telescopes – Glass

Reflecting Telescopes – Mirrors Newtonian Focus Cassegrain Focus

Prime Focus

Spherical Aberration

Spherical Mirror -> Parabolic Mirror

Functions of a Telescope:

1. Gather Light Proportional to Diameter2 10m KECK

5m Palomar 2. Resolution Proportional to Diameter

3. Magnification

Radiation Thermal Radiation Fahrenheit (°F) Celcius (°C) 0°C – Water Freezes 100°C – Water Boils (at sealevel)

Kelvin (°K) 0°K = Absolute Zero K = °C + 273

Blackbodies – Perfect emitter of radiation

Wein’s Law

Stefan-Boltzmann Law

Spectroscopy

Rainbow = Spectrum Violet – Blue – Green – Yellow – Orange – Red 400nm 550nm 700nm

Types of Spectra

 Continuous Spectrum (All colors)  Emission Spectrum (Black except for colored lines)  Absorption Spectrum (Colored except for black lines)

Kirchhoff’s Laws of Spectroscopy

1. Hot opaque gas liquid, or solid gives a continuous spectrum. 2. Hot rarefied (transparent) gas gives a emission spectrum. 3. Light from hot opaque source through hotter rarefied gas gives a absorption spectrum.

9/30/08

Creates Absorption Lines – Absorption of photons by electrons Creates Emission Spectrum – Emission of photons by electrons

Doppler Effect Moving toward you – Shorter wavelength Moving away from you – Longer wavelength

Solar System Planets

 Orbits the Sun  Gravity pulled it into a spherical shape  Cleared its neighborhood of debris  8 Planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Dwarf Planets

 Orbits Sun  Spherical  Has not cleared its neighborhood of debris  5 Planets – Pluto, Eris, Ceres, Makemake, Hauma

Terrestrial Planets Jovian (Giant) Planets Planets Mercury, Venus, Earth, Mars Jupiter, Saturn, Uranus, Neptune Size Small (< 12,800 km) Large (> 49,000 km) Mass Low Large Density High -> Rocky Low -> Gases Rotation Slow Fast Distance Close (< 1.5 AU) Far (> 5 AU) Moons Few Many Rings No Yes

10/2/08

Formation of the Solar System Solar Nebula Model – Clouds of gas and dust ~4.5 billion years ago Accretation – Small objects stick together to form larger ones Protoplanets -> Planetismals -> Planets Angular Momentum – Spin motion Lost Angular Momentum

1. Interaction with early magnetic field 2. Loss of mass from system from early solar wind

Extrasolar Planets – Planets around other stars. Over 200 known using Doppler Shift.

Earth Density – 5500 kg/m3 Surface Density (rocks on surface) – 2000-4000 kg/m3 Albedo – Percent of reflected sunlight - About 37%

Atmosphere Composition

 78% Nitrogen (N2)

 21% Oxygen (O2)

Primary Atmosphere

 Hydrogen/Helium  Escaped to space

Secondary Atmosphere

 Volcanic Activity – Volcanism

 Carbon Dioxide (CO2)

 Water (H2O)  Ammonia (NH3)

Third (Tertiary) Atmosphere

 N2O2

Earth’s Surface (Crust) Formed 4.5 billion years ago. Oldest crust ~3.9 billion years ago Continents – 3.5 billion years old Ocean floor – 200 million years old

10/7/08

Plate Tectonics 3 Types of plate boundaries

 Divergent Boundary – Plates move apart o Earthquakes o Quiet Volcanism  Convergent Boundary – Plates move together o Subduction – one place moves under another . Earthquakes . Explosive Volcanism o Collision Boundary – Pushes up a mountain range . Earthquakes  Transform Boundary – Plates slide past eachother o Earthquakes

Interior

Differentiation – Heavy elements sink while lighter elements rise. Leads to layers. Magnetic Field

Magneto hydrodynamics (MHD)

Charged Particles + Atmospheric Molecules = Light Northern Lights – Aurora Borealis/Aurora Austalius

Moon Tides caused by gravity Differential gravity

Highest High Tides – New/Full Moon – Moon/Earth/Sun Aligned Lowest High Tides – 1st/3rd Quarters – Moon/Earth/Sun Angle 90° – Neap Tides

Effects of Tides Tides and Ocean Floor/Continental friction slows the Earth’s orbit. Eventually 1 day will equal 27 1/3 current Earth days – Synchronous rotation

10/9/08

Mare – Dark color Highlands – Light color Ejecta Blanket Late Heavy Bombardment Period – Early solar system where floating rocks struck planets/moons.

Comparison of Terrestrial Planets

 Orbits o Mercury . 0.4 AU . 88 day orbital period . Most elliptical planetary orbit  Sunlight 2.3x more intense at perihelion o Venus . 0.72 AU . 225 day orbital period . Closest planet to Earth o Mars . 1.52 AU . 687 day orbital period . Very elliptical orbit . Mars & Earth are closest every ~17 years  Rotations o Mercury – 59 day rotation . 3-2 spin-orbit coupling (rotates 3x for every 2 orbits) . Result of tidal forces and very elliptical orbit o Venus – 243 day rotation . Day longer than year . Backwards rotation o Mars – 24.6 hour rotation  Sizes o Earth – 12,756 km diameter (100%) o Venus – 95% (Earth’s Twin) o Mars – 53% o Mercury – 38%  Densities o Earth – 5500 kg/m3 o Venus – 5300 kg/m3 o Mars – 3900 kg/m3 o Moon – 3300 kg/m3 o Mercury – 5400 kg/m3 . Indicates very large Iron core  Magnetic Fields o Mercury – Has current magnetic field o Venus – No magnetic field o Mars – No current magnetic field, but had one in the past  Atmospheres o Mercury & Moon have no atmospheres . Possible Ice deposits at poles . Temperature range on Mercury – 100K to 700K  Largest temperature range in solar system o Venus . 95 atmosphere pressure

. CO2  Extreme greenhouse warming (750K) . Clouds composed of sulfuric acid . Must use radar to “see” surface o Mars . Thin atmosphere  Pressure 6 x 10-3 Atm

 CO2  Temperature range – 210K to 310K  Temperature and Pressure preclude liquid water on surface  Mars has polar caps o Seasonal Cap: CO2 o Permanent Cap: H2O o Exchange of CO2 and H2O between caps and atmosphere o Major driver of Mars climate  Big Temperature and Pressure variations lead to global dust storms o Geology . Earth – Most Active . Venus . Mars . Mercury – Least Active

Mars – Earth-like conditions

 Atmosphere & clouds  Day length same as earth  Seasons  Polar caps  Wave of darkness

10/16/08

Comparison of Jovian Planets

 Orbits o Jupieter . 5 AY . 11.9 Year orbit o Saturn . 10 AU . 29.5 Year orbit o Uranus . 19 AU . 84 Year orbit o Neptune . 30 AU . 165 Year orbit  Sizes

o Jupiter – 11 Dearth o Saturn – 9.5 Dearth o Uranus – 4 Dearth o Neptune – 3.9 Dearth  Densities o Jupiter – 1130 km/m3 o Saturn – 690 km/m3 – Could float on water o Uranus – 1290 km/m3 o Neptune – 1640 km/m3  Interiors o Jupiter/Saturn – H2, Metallic H, Core o Uranus/Neptune – H2, Slush, Core  Rotational Periods o Differential Rotation . Jupiter  Equator – 9h 50m  Poles – 9h 56m  Magnetic Field – 9h 56m o Jupiter – 9h 56m o Saturn – 10h 39m o Uranus – 17h 14m (rotation axis lies on orbital plane) o Neptune – 16h 7m  Discovery o Jupiter & Saturn – Known to ancients o Uranus discovered during routine sky survey by Sir William Herschel on March 13th, 1781. o Neptune predicted to exist. Position predicted by J. Adams and U. Leverrier. Discovered Sept 23, 1846.  Rings o Thick Rings – Formed by destruction of icy moon (Saturn) o Thin Rings – Meteorite bombardment of small icy moons (Jupiter/Uranus/Neptune)

10/21/08

Pluto

 Position predicted by P. Lowell  Discovered by Clyde Tombaugh at Lowell Observatory in 1930  39AU from the Sun  Very elliptical orbit: 19.7AU to 49.3AU  Orbital period: 248.6 years  Orbit inclined 17°  Pluto moves inside Neptune’s orbit (1979-1999)  Within Kuiper Belt -> Dwarf Planet

 Diameter - 19 Dearth  Density – 1800 kg/m3 -> Ice with some rock  Rotation axis tilt - 120° -> tipped on side

Pluto and Charon

 Charon discovered in 1978 as US Naval Observatory in Flagstaff  Pluto and Charon in mutual synchronous rotation: 6.39 days  Series of mutual eclipses between 1985 and 1990

Results from eclipse studies

 Charon about ½ DPluto

 Pluto’s surface contains N2 and CH4 ice. Ice vaporizing near perihelion to produce atmosphere

 Surface of Charon contains H2O ice

Missions to Pluto

 No spacecraft has visited Pluto  New horizons mission: Launched in Jan 2006, will arrive at Pluto in 2015

Eris

 Discovery announced in July 2005, Moon announced in October 2005  Officially named Eris and Dysnomia in September 2006  Eros slightly larger then Pluto  Distance 67.7AU  Very elliptical orbit (Perihelion – 38AU, Aphelion – 98AU)  Orbit inclined 45° to ecliptic  In Kuiper Belt -> Dwarf Planet

Asteroids

 Small rocky debris  All small  Largest is Ceres (954 km). Now classified as Dwarf planet  Formation o Destruction of a small planet? NO! o Material which never accreted into a planet

Comets

 Kuiper Belt – short period P < 200 years  Oort Cloud – Long period P > 200 years  Evolution o Solid & Icy o Loses ice with each pass by the Sun o Eventually mainly dark rocky material  Shoemaker-Levy 9 o Close encounter by Jupiter in 1992 had ripped comet into 21 pieces. Orbit determination showed SL-9 would encounter Jupiter again in July 1994.

10/23/08

Meteorite Material – Small debris

 Floating in space – Meteoroid  Encounters and atmosphere – Meteor o Glow – Shooting star  Lands on surface – Meteorite

Meteor Shower – Large amount of meteors coming from one part of the sky

Meteorites

 Stones  Stony-Irons  Irons  Falls – Seen to fall  Finds – Fell long time ago, picked up much later

Sun

 Star – Produce their own energy through nuclear fusion  Planet – Shine by reflective sunlight  1 AU from Earth = 1.469 x 108 km – Takes light ~8.3min to get to Earth  Density – 1410 kg/m3 – Ball of gas o Normal Gases – lots of particles in motion o Temperature – How fast particles move . 0⁰ K = Absolute Zero  Point when all motion stops at the molecular level o Number Density – Number of particles per unit volume . Luminosity – Total energy emitted from a star every second o Low enough for photons to escape . Opaque -> Transparent  Photosphere – Surface of Sun o Spectrum comes from Photosphere

10/30/08

Corona

 Coronal loop and coronal holes o Solar Wind emanates from coronal holes  Differential rotation o Equator – 25 days o Poles – 27 days  Magnetic field lines get stretched  Field lines become tangled. They can snap and break.  Energy stored in magnetic field lines contribute to coronal temperature

Active Sun

 Short-lives periods of enhanced activity  Sunspots are most active feature of active Sun periods

Sun Spots

 Dark because they are cooler  Sunspots occur in groups  Individual sunspot is about 10,000km across and lasts a few hours to a few months  11-year sunspot cycle o Number of sunspots varies on a ~11-year cycle o Locations also vary during cycle

Prominences

 Huge clouds of H gas  Follows looping magnetic fields associated with sunspots  ~100,000 km in extent  Lasts for hours to weeks

Solar Flares

 Violent burst of energy over all the EM Spectrum  Releases dangerous radiation particles  Lasts no more than a few minutes

Coronal Mass Ejections

 Huge balloon-shaped volumes of high-energy gas ejected from corona  Break through Sun’s magnetic fields

11/4/08

Discover how stars are born live and die

 Begin our study by describing intrinsic properties of stars o Energy Output . Need Distance to know energy output  Parallax . Absolute Magnitudes (not apparent magnitudes) . Apparent Magnitude (m)  1st-6th Magnitudes  With new technology can be negative and have decimals . Luminosity o Radius . o Surface Temperature  Such Properties provide us with an overview necessary to describe stellar lives

11/6/08

Apparent Magnitude – Distance and power combined, star brightness. Absolute Magnitude – Brightness at 10 parsecs.

Luminosity classes

 Size classes o Size is dominating factor in determining luminosity.

Ia Bright Supergiant Rigel Ib Supergiant II Bright Giant Polaris III Giant Capalla IV Subgiant V Main Sequence The Sun

 Measuring Distance o Spectroscopic Parallax . Not actual measurement of parallax . Find star distance that are too far . A way for conventional parallax  Measuring Star Mass o Binary Stats -> Mass of Stars 3 2 . (m1 + m2) = a /p

11/13/08

Interstellar Medium (ISM)

 Gas and dust between stars  99% of gas is Hydrogen  1% is dust

 Gas Clouds  Dust Clouds o Nebula – Cloud of gas and dust  Interstellar Dust o Only 1% of ISM o Can be detected by interstellar extinction and reddening . Interstellar Extinction  Dimming of starlight by the absorption of starlight by interstellar dust. . Interstellar Reddening  Star appears redder then it is because interstellar dust scatters away short wavelength light.  Star Formation o Molecular cloud o Mass -> Gravity o Temperature -> Pressure

 Solar Mass Star (0.08 – 1.4 x Msun) o Molecular Cloud

. Tlow -> Plow  Gas + Dust collisions -> Heat (IR)

 Tcloud starts low -> Plow -> Collapses . Gravity Dominates . Cloud Collapses o Eventually core becomes opaque to IR . Becomes Protostar . Heat from sollisions trapped in star - T↑ - P↑  Differences between massive stars and solar mass star formations o Massive Stars . Higher luminosity and temperature . Strong sources of IR and UV  UV -> H II Region . Large mass associated with stronger solar winds . Protostar stage shorter  Fusion begins earlier o Main Sequence . Creates energy through fusion of H into He (Hydrogen burns) . Stable in size  Differences between solar mass and massive stars on the Main Sequence o Creation of Energy (H -> He Fusion) . Solar Mass – Proton-Neutron Cycle . Massive – Carbon-Nitrogen-Oxygen (CNO) cycle o Transport of radiation in interior o Massive stars use their mass quicker and have shorter lifespans

11/18/08

Evolution of solar mass stars beyond the main sequence

 No energy production -> T↓ -> P↓ -> Star Collapses -> n↑ -> T↑

o Number Density = = n

 Helium core expands into hydrogen and begins burning H again o H-shell burning . T↑ -> P↑ . Expands into Red Giant o Core -> Degenerate Gas . T & P no longer directly related . T↑↑↑ to 100 million K  He -> C (Triple Alpha Process)  Helium-Core Burning  Helium Flash o Several seconds to 350 million K o H-shell used up, core now Carbon, shell now Helium . No Energy Production -> T↓ -> P↓ -> Collapses -> n↑ -> T↑ - > Shell Burning . He-Shell burning into Red Giant again o White Dwarf

Star Clusters

 Open (Galactic) Clusters o Lots of open space between stars o Collection of 10-1000 stars o ~25 pc diameter  Globular Clusters o Stars very close together especially in the central region o Collections of 105 to 106 stars o ~10-30 pc in diameter  Turnoff point provides into about age

Variable Stars

 Cepheids – Massive stars – Period range between 2 and 60 days o Period-luminosity relationship – Longer Period -> Greater luminosity  RR Lyrae Stars – Lower mass stars. Period < 24 hrs. all RR Lyrae stars reach some peak luminosity  Both Cepheid and RR Lyrae stars change luminosity because of change in size

Planetary Nebulae

 Strong stellar winds rip away outer layers of star  Caused by helium shell flashes  Expelled gas forms ring around core – called a planetary nebulae  Left-over core is a white dwarf

Evolution of massive stars (M < 1.4 Msun)

 Everything same through second Red Giant stage

o 1.4-8 Msun . Solar winds blow off enough mass to drop below 1.4 Msun and continue as a normal star (Nebulae -> White Dwarf)

o M > 8 Msun . H -> He -> C -> O -> Ne -> Mg -> Si -> S -> Ar -> Ca -> Ti -> Cr -> Fe  Just know: H -> He -> C -> Other Stuff -> Fe . Supernova -> Explosion of star  Ball of Neutrons left (Neutron Star)  Black Hole left

12/2/08

Black Holes

Rs – Schwarzchild Radius – When the escape velocity reaches the speed of light Singularity – Point where all mass is concentrated (center of the Black Hole)

Event Horizon – Info escapes at distance greater then Rs and cannot escape if closer then Rs

Non-rotating – Matter hits singularity Rotating – Kerr – Wormhole – Passageway

Detecting Blackholes Binary Star System – Xrays Gamma Ray Bursts – Forming of a Black Hole

Galaxies – Gas, stars, dust, planets, etc held together by gravity

Milky Way Galaxy

 Location in Galaxy o 26,000 LY from center o Finding our location . RR Lyrae Stars  All reach same peak luminosity  Common in globular clusters

Metal – Element heavier then He

High Metal Content Stars – Population I Stars – Found in the Disc Low Metal Content Stars – Population II Stars – Found in the Halo

Bulge Population I & Population II Stars Lots of gas and dust Some stars still forming

Halo Population II Stars Globular Clusters Little gas and dust No active star formations

Disc Population I Stars Lots of gas and dust Active star formation Open Clusters

Nucleus

Center – Sagittarius Astar (SGT Astar) Surrounded by gas and dust Super Massive Black Hole 6 2-4 x 10 Msun Dark Matter – Mass only detected by its gravity Massive Compact Halo Objects (MACHOs) Massive Weakly Interacting Particles (WIMPs)

12/4/08

Finding Distances to Galaxies

 Cephid Variables (< 80 M LY)  Spectroscopic Parallax with OB stars and Type I supernovae (<680 M LY)  Typical Galaxy Luminosity (<799 M LY)

Hubble’s Law

 V = Hd o H = 71 km/s/Mpc (Hubble’s Constant)  Universe is expanding

Galaxies grouped into galaxy clusters – Ours is the “Local Group” Galaxy Clusters are grouped into Superclusters – Ours is the “Local Supercluster”

Active Galaxies and Quasars Galaxies with higher than normal luminosity Radiation typically does not peak at optical wavelengths Energy comes from nucleus of galaxy Active Galactic Nuclei (AGNs)

Evolution of Galaxies

 QSOs o Seyfert . Normal Spiral o Radio . Normal Elliptical

Cosmology

 Study of the Universe’s origin, structure, and evolution  Model must explain: o Expansion of the Universe o Why/How everything is Evolving  Age given by 1/H o Best estimate – 13.7 Billion Years

Big Bang

 Explosion which started the universe expanding  Start of the universe and start of time  T > 1032 K, no matter, just radiation  As universe expanded, T declined Radiation and Matter

 E=mc2 – Matter created from energy  Within 4 seconds after the Big Bang, all protons, electrons, and neutrons in the universe formed  Neutral atoms formed about 500,000 years after the Big Bang. Matter then dominated the universe