Physics 406 Course Review J.V. Hollweg, E. Möbius

Bring the review with you each day to class. You may insert comments of your own. Some space has been left at the end of each major sub-chapter.

These review sheets should be used to study for the exams. Many exam questions will be directly based on these pages. They are not to be memorized, but they should serve as a guide to what you are expected to understand. However note, the Review won't replace the book! As you can see it uses a “sound bite” format. Therefore, read your course book!!! Ask questions, if you don't understand what is in the Review!!! • Consult your course book • Ask questions in class. They are appreciated!!

Revised E. Möbius, 1/2003 0. Roots of Astronomy and our View of the World

Why does Man study Astronomy? organize time (plan the year) -> clock, calendar, seasons understand how the world is built -> model of the universe - We face discussions between Science and Religion Where do we come from? - We are confronted with the limitations of Science Will we ultimately understand ”everything”? In astronomy almost all sciences are used Mathematics -> sizes, "language for modeling" Physics -> understand processes Chemistry -> composition of planets and comets Geology -> appearance and evolution of planets Meteorology -> planetary atmospheres Biology -> life on Earth and elsewhere? Contents of the Universe Planets, moons, comets Sun and stars, gas nebulae Clusters of stars, galaxies, clusters of galaxies Learning goals • Astronomy spans all sciences, in particular all branches of physics • Physics is the art to measure objects and processes • Science is a never-ending enterprise • Contents of the universe

2 I. Use of Scientific Methods

Chapter I. is to be used as a Compendium throughout the Course. We browse through it now and fill in some blanks when we use the tools in the following Chapters. 1) To Measure Means to Compare We measure an unknown quantity by comparison with a known quantity. A. Powers of ten

Large and small numbers are presented easier as powers of ten: e.g.: 2,300 -> 2.3 . 103; 0.000,000,2 -> 2 . 10-7 B. Geometry a) Length: Basic Unit: m (cm, km) Compared with a meter stick (original meter, Paris) Size and Distances of Planets inin the Solar System

Geometric model 1:10,000,000,000 ______

Reality Model Size Distance Size Distance in km in km in cm in m ______

Sun 1.4 . 106 13.9

Mercury 4880 5.8 . 107 0.05 5.8 2 steps up Venus 12100 1.0 . 108 0.12 10.8 7 steps up Earth 12760 1.5 . 108 0.13 15.0 Rear of auditorium Mars 6800 2.3 . 108 0.07 22.8 Tree in front of auditorium Jupiter 143800 7.8 . 108 1.44 77.8 UNH bookstore Saturn 120000 1.4 . 109 1.20 143. EOS (Morse Hall) Uranus 50800 2.8 . 109 0.51 287. Hood House Neptune 49500 4.5 . 109 0.50 450. Tin Palace Pluto 2300 5.9 . 109 0.02 590. Young's Restaurant ______Closest Star: LY a Centauri 4.34 4.1 . 1013 4,108,799 San Francisco ______

3 Further units derived from Length: -> Area = Length * Length m * m = m2 Used for example for Surface of objects E.g.: circle 2x in radius -> area of circle: 2*2 = 4 x as large!!

-> Volume = Length * Length * Length m * m * m = m3 Used for example for Volume of objects E.g.: sphere 2x in radius -> volume of sphere: 2*2*2 = 8 x as large!! b) Angles: Degrees (360o per circle) (90o right angle) Minutes (60' per degree) Seconds (60'' per minute) c) Distance/Size determination in Astronomy: To get distances and sizes in astronomy we use angle measurements and a baseline. Skinny triangle: (in Astronomy always a "skinny triangle") i) Distance r known ii) Observer separation d known r obs.1 r observer q d d q obs.2 "Parallax" -> Determine i) Size d ii) Distance r of an astronomical object q = 360⋅ d = 57.3⋅ d by measuring q, plugging into: 2p r r and solving for d or r "Parallax" is a fundamental method to measure distances in Astronomy. Useful length units in astronomy: Longest Baseline for Parallax: 1 AU [Astronomical Unit = Earth - Sun distance] = 1.5 108 km Distance from which 1 AU is seen as 1 arcsec 1 Parsec = distance giving a Parallax of 1 arcsec = 3.1 1013 km = 3.26 LY Distance based on the speed of light 1 LY [Light-year = distance light travels in 1 year] = 9.5 1012 km

4 C. Action: a) Time Basic unit: sec (second), hour, day Time is measured by comparing with a regular motion. Method Type of Clock Accuracy sun throwing a shadow -> sun clock -> hours sand flowing through an orifice -> sand clock -> minutes mechanical pendulum -> mechanical clock -> second oscillation of crystal -> quartz clock -> fractions of second b) Velocity: Derived Unit: m/sec km/h Distance traveled per unit time: Velocity = Distance/Time Change of velocity (acceleration, deceleration) Derived Unit: m/sec/sec = m/sec2 Velocity change/unit time: Acceleration = Velocity/Time D. Substance Chapter IV a) Mass "amount of material" Basic Unit: kg (kilogram) Compared with original kg (Paris) Mass articulates itself in two ways:

Inertial mass mi resists the attempt to move it Gravitational mass mg ability of objects to attract one another mi = mg Einstein's General Theory of Relativity Note: Do not confuse Mass with Weight!! Weight means a force in a given gravitation (e.g., on Earth) Mass of the same body remains the same, but its Weight may vary from location to location (on Earth, Moon or in free space)!!! Unit: see Force (or 1 kilopond (kp) = 1 kg on Earth) b) Mass density: = mass/volume Derived Unit: kg/m3 -> Idea of planet's interior: rock + iron core -> denser than rocks or of stars' interior -> compressed gas or neutron stars -> denser than atomic nuclei c) Force ability to pull or push an object (to change its motion) Derived Unit: kg * m/sec2 = Newton (N) in Chapter IV d) Energy Ability to change motion or generate heat Derived Unit: kg*m2/sec2 = Joule in Chapter IV Types of energy: Gravitational, kinetic (motion), heat all interchangeable (in principle): For example: Falling object vaporizes rock -> explosion -> round crater Gravitation ﬁ Motion ﬁ Heat

5 e) Pressure = Force per area in Chapter VIII Derived Unit: N/m2 = Pascal ≈ 1/50 Pounds/foot2 Holds things up against gravity: Atmospheres: pressure = weight of overlying atmosphere Stars: internal oven keeps material above in balance Black holes: no pressure high enough to keep it from collapse? f) Temperature Average energy per molecule in Chapter VI, VIII Basic Unit: Kelvin = Centigrade + 273 (starts with 0 degree!!) 0 Kelvin = -273 Celsius = - 404 Fahrenheit 273 Kelvin = 0 Celsius = 32 Fahrenheit Provides ability for gas to resist gravity ﬁ Determines properties of atmospheres hot sun has an extended atmosphere warm earth's atmosphere is only tens of miles deep hot and small Mercury with its weak gravity lost its atmosphere Determines life of stars Stars form from collapse of cool interstellar clouds ("stellar nurseries") Nuclear Fusion possible in hot interior of stars ("ignition temperature")

System of Units

Basic Units

Length 1 Meter Time 1 Second Mass 1 Kilogram [m, cm, km] [sec, msec] [g, kg]

Based on: Wavelength of light of Kr Frequency of Cs atoms Mass of C atoms atom (Original kg in Paris) (Original m in Paris)

Derived Units

Area = Length * Length [1 m2 ] Density = Mass/Volume [1 kg/m3 ] Volume = Length * Length * Length[1 m3 ]

Velocity = Length/Time [1 m/sec] Force = Mass * Acceleration [Newton] 1 N =1 kg m /sec2 Acceleration = Velocity/Time [1 m/sec2 ]

6 2) What we measure Getting information over large distances in astronomy: in Chapter V A) Electromagnetic radiation: Contains key information on what is happening out there radio, microwave, IR, light, UV, X, gamma rays B) Particles: Cosmic rays (sample of Milky Way Galaxy material) Meteors (sample of early solar system material) Comets (sample of early solar system material) Solar wind (sample of sun material) C) Forces: Gravity (the key to deducing masses)

3) Deduction We use Deduction, i.e. we measure something to deduce something else: We measure Make use of Deduce

A) angle ﬁ size or distance skinny triangle

B) orbits ﬁ masses in Chapter IV knowledge of gravity

C) color ﬁ temperature in Chapter VII blackbody (red:cool; yellow:hot; blue:very hot)

D) change in frequency ﬁ velocities in Chapter VII Doppler shift (frequency increases -> moves toward us; frequency decreases = moves away).

7 4) Scientific Reasoning We use Scientific Reasoning to test our view of the world and to develop new measurement methods. Scientific Reasoning consists of: i. Hypothesis ii. Prediction iii. Test A) i Earth goes around sun. ii. Prediction Aberration of starlight in Chapter V (analogy: raindrops seen from moving car) iii. Test Bradley (1726 - 1728): first proof that earth goes around sun ii. Prediction Stellar parallax in Chapter VII iii. Bessel 1838 -> first determination of distance to a star B) i. Earth rotates on its axis. ii. Prediction Coriolis force - apparent force as earth rotates iii. Test Foucault pendulum (1851): first proof of earth's rotation. (Coriolis also gives circulation of weather systems.) (Jupiter's red spot and Neptune's dark spot have circulation of high pressure systems.) C) i. Mercury & Venus orbit sun. in Chapter III

ii. Prediction Phases full to crescent (like moon) iii. Test Galileo 1610 (observed with telescope)

8 5) Scientific Models To understand the universe and its contents we build models of what is going on. A) Geometric models in Chapter III Geometry is maintained, length scales reduced to fit - globe -> Earth - map -> orientation in surrounding area B) Physical models Description of causal interaction of objects (e.g. with gravity, magnetism etc.) -> constant improvement of models is what we do in Science Overview of Scientific Methods

Method What is it? Example Measurement Comparison with known Length <-> meter stick (size, amount, ....) Model Describe results with something Geometric model: something that we can map of Earth visualize or imagine small solar system model Scientific i. Hypothesis how something i. Angle and distance of object Reasoning works are related ii. Prediction what happens ii. Smaller angle means farther away iii. Test of prediction iii. Measure size + distance Deduction i. Measure something from i. Measure Angle to object the ends of a Baseline + Length of the Baseline ii. Determine something else ii. Determine Distance of object

Learning Outcomes: In the beginning: 1. A) through D) b), 2), 3) A), and 4) A) Other items will be included as course proceeds! • Use of Powers of Ten • Define length, area, volume, angle, mass, mass density and weight • Use of these quantities in astronomy • How to determine distances and sizes in astronomy (Parallax) • Use of radiation, particles and forces to measure astronomical quantities • What is deduction? example: parallax to determine distances • What is scientific reasoning? examples: Earth moves -> parallax and aberration of stars

9 II. What We See in the Sky 1. Celestial Sphere with "fixed" stars The stars don't change their position with respect to each other. A) Orientation on Earth and sky Determine position on celestial sphere like on the globe (sphere of the Earth) Parallel: lines parallel to the equator (Durham lies on 43th parallel, 43o north of the equator) stars apparently move along parallels over the sky Meridian: lines from south pole to north pole line from south overhead to north We use the same lines as on the globe projected onto the sky Earth (Globe) Sky (Celestial Sphere) Poles (N, S) Celestial Poles (N, S) Equator Celestial Equator Parallels Parallels Latitude Declination Meridian (local N-S line) Meridian (dto.) Longitude Right Ascension

TheThe CelestialCelestial SphereSphere Meridian

Zenith Height NCP

Horizon W Observe S r N Eart E h Azimuth

Celestial Equator

Declination

10 B) Coordinates in the sky:

a) North Celestial Pole (NCP) (always above horizon in Durham). South Celestial Pole (always below horizon in Durham). Celestial Equator (only 1 half above the horizon) b) Declination: degrees N or S of celestial equator (like being on a certain Parallel)

c) NCP at 90o N of equator -> height of NCP above horizon = latitude of observer. View North

Northern Celestial Pole Meridian Celestial Equator

Declination

o 43 47 o= 90o - 43o

W N E Durham o NCP 43 Latitude

N Horizon S Horizon

11 2. Apparent rotation of the sky from East to West (Earth turns W to E = counterclockwise, when we look down onto northern hemisphere) A) How do stars on certain positions move over the sky?

a) On celestial equator: pass through horizon due E, due W. are up 1/2 day; and down 1/2 day. b) On N declination: are up more than 1/2 day, stars are high in sky when on meridian stars rise in NE and set in NW on far North declination: stars never set (examples: Big and Little Dipper) c) On S declination: up less than 1/2 day, star is low in sky when on meridian star rises, sets: SE, SW on far South declination: stars never rise d) Daily motion: object is always highest in sky when on meridian. B) Sidereal day Refers to return of a star from due S on one day to due S on the next day: sidereal day = 23h 56m 4s -> shorter than solar day -> Sun is not fixed in the sky relative to the stars

12 3. Sun. A) Apparent annual eastward motion with respect to the stars. Observable consequences: a) Solar day (noon to noon) is longer than sidereal day. * star * sun *

stick or meridian

E S W E S W E S W start one sidereal day one solar day

To Stars 1 = start 2 = sidereal day 3 = solar day

sun

Earth's Orbit

2 3 1 N N

Eastward motion of sun is due to: Earth orbits sun in one year, counterclockwise looking down from north. b) Westward progression of a specific constellation in the sky during year Constellation sets and rises earlier every day After some time a constellation which is east of the previous one is seen at the same position in the sky, when observing at the same time of the night. c) Sun's motion across the sky completed after 1 year -> Definition of one Year B) Change in declination during year: Observable consequences: a) Rising and setting points on horizon (more N in summer than winter) b) Length of daylight. c) Height of sun at noon.

13 All the above values are different for different latitudes on Earth! d) Declination of sun on the celestial sphere Dec. 22 decl. = -23 1/2 deg. winter solstice March 20 decl. = 0 vernal equinox June 22 decl. = +23 1/2 deg. summer solstice Sept. 23 decl. = 0 autumnal equinox The Declination is the same for all observers at the same time!

N TO SUN N

23.5 TO CELES. EQ. 23.5 TO CELES. EQUATOR

S S TO SUN JUNE 22 DECEMBER 22

N TO SUN

TO CELES. EQ.

TO SUN S MARCH 20 , SEPT.23

C) Ecliptic: apparent annual path of sun with respect to the stars. The ecliptic - runs through the constellations of the Zodiac - is a Great Circle on celestial sphere - has an Inclination of 23.5o relative to celestial equator

Due to: - Earth's orbit planar and sun in the plane fi Great Circle. - Earth's axis tilted relative to orbital plane fi Inclination. (This observation does not prove that the earth goes around the sun) This leads to Seasons: Height of sun in sky at noon fi more direct sunlight in summer etc. Length of daylight varies Climate Zones Arctic, Antarctic (sun up in summer, down in winter) N, S temperate (regions with significant change of height of the sun) Tropics (sun always high)

14 to north celestial pole

to celestial equator N N to ecliptic 23.5 to ecliptic SUN S S

JUNE 22 to celestial equator DECEMBER 22

D) Sun clock is not exact over the year (called Analemma)

Solar day not exactly 24h (varies over the year) but annual average very close to 24h This is due to: Ecliptic is at oblique angle to equator Earth's orbital speed changes Earth - sun distance changes over the year

15 4. Moon A) Apparent motion of the Moon a) Eastward with respect to sun and stars Due to: Moon orbits counterclockwise when looking down onto northern hemisphere. Moon's orbital period shorter than Earth's b) Phases: Sunlit side 'points' toward sun.

to sun

Crescent moon close to sun: sets soon after sunset (waxing crescent) or rises shortly before sunrise (waning) Full moon opposite to sun: rises at sunset; sets at sunrise Boundary between light and dark on the moon is an arc -> Early proof that moon is spherical Half moon at right angle to the sun in the sky -> Early deduction that Sun is very far away & very large. Earth shine observed on new moon and crescent -> Sunlight reflecting off Earth onto moon (daVinci ca. 1500) c) Synodic month (refers to phases) Longer than sidereal month (Moon in same position w.r.t. the stars) Synodic month originally used as definition of Month From month to month each phase (e.g. full) of the moon progresses eastward through the stars.

moon's orbit (eastward)

earth full moon to distant start sun N stars

full moon 1 synodic month later earth to distant N stars

1 "month" sun moon one sidereal month later; later not yet full

apparent eastward motion of sun B) Moon's orbit a) Great circle (almost) close to ecliptic -> Full moon opposite sun: high in sky in winter, and low in sky in summer, 16 Moon's orbit is inclined 5o to the ecliptic Moon's path on celestial sphere Node

5 deg Ecliptic Node

Due to: Moon's orbit and Earth in one plane ﬁ Great Circle. Moon's orbital plane inclined to Earth's orbital plane ﬁ Inclination.

b) Nodes progress westward Due to: Sun's gravitational pull on Moon. Full cycle = 18.6 years (determines when eclipses occur). C) Eclipses Reason -> shadow play (Sun, moon, Earth exactly aligned!) Solar eclipses during new moon. Lunar eclipses during full moon. But not every new or full moon, only when new or full moon near ecliptic (i.e. node). Eclipse seasons: Line of nodes must be toward sun. About 6 months apart (less than 6 months) a) Lunar Eclipses: Types: Partial (Earth's shadow line seen on moon) Total (No direct sunlight on moon) But: moon not completely dark during total eclipse -> some sunlight reaches the moon through the Earth's atmosphere Uses of lunar eclipses: - Early proof that Earth is spherical (curved shape of shadow line) - First measurement of moon's size and distance (size of Earth's shadow) b) Solar Eclipses: Types: Total (sun fully covered by moon) Annular (ring of sunlight, varying with distance of the moon) Partial (Sun and moon not exactly aligned) Uses of full eclipses: - Study solar atmosphere in Chapter VIII much fainter light of the upper layers of the atmosphere becomes visible We see: sunlight scattered by electrons & dust

17 Sun (covered) sunlight electron

scattered sunlight Us

- General Relativity in Chapter X (Bending of starlight by gravitational forces)

18 5. Calendar Based on

A) Sun -> day (one circle over the sky) -> year (journey along the ecliptic) = 365.24 days B) Moon -> month (≈ one full cycle of lunar phases) sidereal month ≈ 28 days; synodic month ≈ 29.5 days C) All "wandering" objects in the sky (as known in ancient times) -> week 7 days ≈ 1/4 of a month Symbolic association of wandering objects with days Day Object Relation in other languages Sunday Sun Monday Moon Tuesday Mars (Mardi in French) Wednesday Mercury (Mercredi in French) Thursday Jupiter (= Thor in Germanic heaven) Friday Venus (Vendredi in French ) Saturday Saturn BehindBehind OurOur CalendarCalendar Decreasing Period Saturday

Monday

Saturn Thursday (Thor) Moon 22 21 15 Jupiter 14 8 7 1 23 2013 6 2 9 16 (Mercredi) Mercury Wednesday 3 12 5 4 10 19 11 Venus 17 24 (Vendredi, Freya) 18 1 Mars Friday Sun

Tuesday (Mardi)

Sunday

Hours of the Day First Hour of the New Day

19 6. Planets Apparent motion of planets with respect to the sun and stars. Always close to ecliptic (They are seen in the southern half of the sky over Durham) A) Appear to move through the stars on nearly great circles close to the ecliptic Due to: The sun is in the center of the orbital plane of the planets. Planet orbits are inclined to Earth's orbit, but not by much. Mercury, Venus always appear close to sun (inferior planets) Mars, Jupiter, Saturn can appear far from sun (superior planets) B) Mercury, Venus We can see them either right before sunrise or right after sunset:

ii iv "evening "morning star" star"

v iii S iii i N N S horizon horizon sun sun

We define: i. Superior Conjunction with Sun invisible ii. Maximum Eastern Elongation "evening star" iii Inferior Conjunction with Sun invisible iv. Maximum Western Elongation "morning star" v. Superior Conjunction with Sun invisible

iv eastward

sun i,v iii N Earth, looking down Merc. onto northern or Venus ii hemisphere orbit

Best time to see Mercury: At maximum Elongation in particular in Spring after sunset or in Fall before sunrise Synodic period: (e.g. from one inferior conjunction to next inferior conjunction) as seen from Earth with respect to the sun Sidereal period (orbit around sun with respect to stars; the planet's 'year') as seen from the sun with respect to the stars Synodic longer than sidereal because earth moves too (everything counterclockwise). Apparent motion in the sky mostly eastward (along with sun) with respect to stars.

20 C) Mars, Jupiter, Saturn.

Apparent motion always westward with respect to sun, but: mainly eastward with respect to the stars. (like sun).

"morning "evening star" star"

horizon horizon N S S N sun sun

We define: i. Superior Conjunction with Sun ii. Emerges as morning star iii. Western quadrature - on meridian @ sunrise iv. Opposition - opposite sun; rises at sunset, on meridian at midnight Best time to observe -> closest to Earth -> brightest Winter opposition best: high in sky (like full moon) (The constellations of the Zodiac are high in the sky on winter nights and low in the sky on summer nights.) v. Eastern quadrature - on meridian @ sunset vi. Approaches sun as evening star vii. Superior Conjunction

eastward v vi sun i,vii iv superior planet ii earth's iii orbit

Apparent motion of M., J., S. is eastward with respect to stars except near opposition --- The motion at opposition is called "Retrograde": Apparent westward motion with respect to stars as Earth speeds by the planet (Planets draw loops in the sky with respect to the stars) After one Earth year the planet appears further east with respect to the stars: Due to: All planets orbit the sun counterclockwise when looking down onto northern hemisphere.

21 III. Geometrical Models of the Universe 1. Old Ideas -

A) Paradigms Man central -> Earth in the center of the universe Heavens perfect and unchangeable -> motion on perfect circles B) Ptolemy -> moon, sun, planets, and stars move on consecutive spheres about Earth Thus the planetary orbits have to follow: -> complicated model with motion on epicycles to explain the loops 2. New Ideas - A) Copernicus (de Revolutionibus 1543) Sun in the center; all planets (incl. Earth) in orbits around the sun moon around Earth (still everything in perfect circles!) B) Pros and Cons Pro: Fewer assumptions in the model: Natural explanation of retrograde motion of the planets (no epicycles!) Natural explanation of Venus, Mercury being always close to the sun Larger sun in the center of the motion Con: Throws Earth out of the center (gets opposition by church, non-scientific) Predicts apparent motion of stars due to Earth's motion (Parallax) However, not observed at Copernicus' time Tycho Brahe: made the best observations of stars and planets at that time but did not see motion of stars -> scientific argument against orbiting Earth C) Evidence supporting Copernicus: a) Galileo (≈1610): put things to a test (by using the first telescope for the sky): - Sunspots fi sun rotates, thus Earth might rotate too - Jupiter and moons fi miniature Copernican system - Venus' phases fi can only be explained by Copernicus' model - Sun and moon imperfect (sunspots, craters) fi heaven is not perfect

b) Supernova ﬁ things in heaven change

c) Aparition of comet ﬁ things in heaven change

22 D) Model makes new predictions - Can calculate sidereal periods of planets (given the synodic periods) - Can calculate relative distances of planets (using geometry) Easy for Mercury and Venus: Sun, planet, Earth -> rectangular triangle at max. elongation Criteria for Scientific Models:

Criteria Ptolemy Aristarch Evidence for a good Model Copernicus (+ Galileo) Assumptions Earth stands still Earth rotates Sun rotates a) (sunspots) b) Objects rotate about Earth orbits about Jupiter's moons the Earth Sun -> mini solar system Scientific: 1) explains √ √ exact positions in observations sky 2) minimizes epicycles no additional retrograde motion assumptions Mercury, Venus orbit Mercury, Venus about special points always close to Sun 3) new tools - relative distances variing brightness of of planets planets over orbit 4) makes Stars stand still Stars go with Not before 1835!!! predictions Earth's motion (Parallax) Venus never more Venus' phases seen than 1/2 lit Venus shows all with telescope! phases as the moon Non Scientific Earth central Sun (large) central relative size (E.- S.) Heaven is perfect Earth is part of the Supernova sun's system, i.e. Comet, Sunspots, similar Craters on Moon

23 3. Kepler Abandoned circles on observational evidence using excellent material of Tycho Brahe Kepler's Laws i. (1609) Planets on Elliptical orbits; sun @ one focus ﬁ sun special ii. (1609) Planet-Sun line sweeps equal areas in equal times Implies that each planet speeds up as it gets closer to sun Explains that seasons have different lengths length of solar day varies over the year iii. (1619) Period - Distance Relation for all the planets (average distance in AU)3 = constant * (period in years)2 (Applies also to Jupiter's moons ﬁ laws "universal", different constant) Implies that Mercury's orbital speed is higher than Venus' speed etc. "Keplerian orbits": small objects orbiting a large 'central' object Important characteristic (we will use this later very often!!): orbital speeds decrease at greater distances from the central object

24 4. Sizes and Distances A) Relative distances a) Sun much further away than moon was derived from the fact that Sun and moon are almost at right angle for half moon (Aristarchos) b) Distances of planets in units of the Earth - Sun distance (Copernicus) -> if any absolute distance known -> all distances known B) Absolute distances Local comparison with meter stick is needed to get absolute distances. to measure the universe we start with the size of the Earth a) Size of the Earth: First measurement (Eratosthenes) - sun under different angle from different locations on Earth - angle and distance of locations -> circumference of Earth -> diameter b) Get any absolute (i.e. km) distance in the solar system: - distance to moon from lunar eclipse compare the size of Earth's shadow (= size of the Earth) with size of moon -> diameter of moon with angular size of moon -> distance of moon - use Earth as a baseline for parallax measurements (from 2 points on Earth) Richer and Cassini (1672) -> derived parallax for Mars Later transits of planets through the disc of the sun were used - modern method: radar reflections off planets Measure time between emission and return of radar signal with speed of light -> distance of object c) Planetary sizes with known distance measure angular size of object -> size of object

25 IV. Physical Models 1. Galileo (ca. 1610) Performs physical experiments with falling bodies and balls rolling down a track concludes that velocity increases (or decreases) under action of force 2. Newton (ca. 1700) A) Basic laws of mechanics:

1st Law) Without any forces an object remains in its natural state: rest or constant straight motion 2nd Law) A force accelerates an object with the mass as multiplicative constant Force = Mass * Acceleration F = m * a 3rd Law) Interaction of two objects Action on one -> equal and opposite Re-action on the other Force = Counterforce B) Universal law of gravitation: a) Universal force on all bodies on Earth objects -> falling to ground by gravity Concludes that: acts also at distance from Earth moon -> falling towards Earth by gravity -> gravity bends natural straight path into circle Note: Force is necessary to constantly change the natural straight path into a circle!! centripetal force (pulling toward center) = gravitational force is balanced by centrifugal (pseudo)-force of motion b) Force decreases with distance Force spread over surface area -> decreases with square of the distance c) Involves masses Center mass pulls: -> force proportional to mass in center Mutual attraction (Newton's third law!) -> both masses in formula m m1 2 2 F F Force = G*Mass1*Mass2/Distance distance

G is the gravitational constant and must be measured

26 d) Explains: Kepler's 3 Laws i) Kepler's 1st Law Ellipses found as natural orbits in gravitation ii) Conservation of energy Kinetic energy + gravitational energy = constant (each planet separately) Gravitational energy increases with distance from sun -> Kinetic energy (i.e. Velocity) of each planet decreases as it gets further from sun iii) Conservation of angular momentum (analogy: ice scater performing pirouette) Angular momentum = constant (for each planet separately). ii + iii) -> Kepler's 2nd Law Equal areas These conservation laws apply also to moons orbiting planets. iv) Provides interpretation for the Constant in Kepler's 3rd Law: For small bodies orbiting a heavy central object (planets around sun or star) [M in solar masses] * (period in years)2 = (average distance in AU)3

But:Mutual attraction revises Kepler's 3rd Law: (Use the sum of all masses!) 2 3 [(m1 + m2) in solar masses] * (period in years) = (average distance in AU) or for circular orbits: (m1 + m2) = (1/G)(velocity1 + velocity2)2 * (distance) For example: Earth speeds with ≈ 30 km/sec at 1 AU Note: Large velocities require large masses to keep things from flying apart! Spinoffs: predicted return of Halley's comet Astronomy ﬁ spawned new physical laws

27 3. Uses of gravity: A) Weigh celestial bodies!! But: With what to compare? Or: which are our weights for the celestial scale? a) Weigh Earth first -> get G (gravitational constant!) Compare gravitational pull of known Mass with pull of Earth MEarth 6 . 1024 kg b) Deduce other masses from:

Orbits of fi m 1 + m 2 . Moons fi Planet's mass 1.9 . 1027 kg (Jupiter) Planets fi Sun's mass 2 . 1030 kg Binary stars fi Stars' masses ≈ 0.1 - 60 Msun Stars in a cluster fi Cluster's mass ≈100 - 100,000 Msun Stars in a galaxy fi Galaxy's mass ≈107 - 1012 Msun Galaxies in a cluster fi Cluster's mass ≈ 1012 - 1015 Msun -> Outlook: "Missing Mass Problem" or "Dark Matter Problem": Masses of galaxies and clusters determined from gravity are much larger than the masses we "see" in the universe B) Find unseen objects: a) Small deflections of planet/spacecraft trajectories fi masses (of planets, moons; Halley's comet) from mutual attraction Example: Deviation of Uranus' orbit -> Discovery of Neptune (1846) Spinoff: fancy math (Calculus, 19th century) still used today b) If a visible star etc. wiggles -> it has a companion Star's position wiggles fi astrometric binary fi discovery of White Dwarfs modern method to find "planet" around star (51 Pegasi) Star's velocity wiggles (Doppler) fi spectroscopic binary modern method to find "planet" around a pulsar C) Slingshots: Spacecraft trajectories: Voyagers, Galileo, Ulysses, Solar Probe use gravity to change the energy (works because the planets are moving) and angular momentum of the spacecraft. Ulysses used gravity to "tip" the angular momentum of the spacecraft. Natural examples: Periodic comets with apogee near Jupiter their orbit was changed by a near encounter with Jupiter Capture of comets into orbit around Jupiter (moon assist) collision with Jupiter (Shoemaker - Levy)

28 4. Earth - Moon System A) Mutual attraction -> combined rotation about gravity center MEarth ≈ 80 * MMoon -> center of combined rotation = center of gravity inside Earth B) Tides: a) Daily tides: 2 high tides and 2 low tides per day Due to: 1/(distance)2 dependence of gravity and combined rotation on the side of the moon gravity creates bulge on the opposite side centrifugal force creates the bulge

Earth rotates under tidal bulge Water closer to moon low pulled away from earth

high Earth high Moon Earth closer to moon low and leaves this water behind

Tidal day = solar day + 50 minutes (approximately). Due to: Moon orbits Earth in same direction as Earth rotates on its axis. b) Sun's gravity also plays a role: -> Due to Moon's pull (2/3) and Sun's pull (1/3) of Tides -> Greater tides when Earth, Moon and Sun lined up (new or full moon) Variation of gravity with distance: -> Greatest tides when Moon closest to Earth at new or full moon c) Consequences of the tides i) Synchronous rotation of the moon (e.g. we see same face of our moon) because: moon's sidereal day = sidereal month or: period of moon's rotation = period of moon's orbit The moon started rotating rapidly It's tidal bulge lagged due to internal friction:

initial fast rotation

weak pull earth moon

strong pull

29 This slowed down the moon's rotation until synchronous rotation was achieved. The process has stopped now. The moon's tidal bulge now points toward the Earth because of its synchronous rotation. ii) Earth's rotation is gradually slowing down (2/1000 sec/century) Cause: the same process as in (i) now acting on Earth's tidal bulge iii) The moon is gradually moving further away from Earth (4cm/year) Cause: Earth's rotation slows down fi Earth loses angular momentum fi moon must gain orbital angular momentum fi moon moves away

earth's rotation

moon's orbit strong strong earth small net force in direction of moon's orbit increases moon's orbital energy and ang. momentum weak weak moon

C) Precession of the Earth's Axis Earth tumbles like a spinning top under the moon's gravitational pull because: Earth is not an ideal sphere flattened by centrifugal force Consequence: NCP moves around with period of 26,000 years -> Vega = polar star in 12,000 years

30 V. Tools in Astronomy and Astrophysics

So far used light and our eyes to gain information about the sky: Limitations: Sensitivity Resolution of our eyes Range of "Colors" Problems with optical trickery To improve we need: -> knowledge about light -> provide better tools 1. Light etc. A) Changes of the light path a) Reflection light rays bounce off a plane like an elastic ball (mirror reflection) incoming angle = exit angle b) Refraction light is bent at the interface of two different materials entering "denser" material (glass) -> towards surface normal exiting "denser" material (glass) -> away from surface normal explained by light as a wave (wave front changes direction with speed change) B) Light is a wave Definitions: Wavelength: distance between 2 wave crests Frequency: number of wave crests passing by in 1 second -> Wave Speed = Wavelength * Frequency Speed of light is finite, but incredibly fast: c = 300,000 km/sec measured by Ole Roemer from orbits of Jupiter's moons (information on moon's position comes later when Jupiter is on the far side of the sun)

31 2. Optical telescopes A) Lenses and curved mirrors Collect and concentrate light Produce images of distant objects at one focal length away B) Design of Telescopes: Objective -> to gather light and produce an image of the object Eye piece -> to serve as magnifying glass to look at the image Use of lenses for objective and eyepiece -> Refractor Use of a mirror for the objective, lens as eyepiece -> Reflector C) Powers and Limitations of Telescopes: PowersPowers ofof TelescopesTelescopes Powers How to improve Limitation Way out

Active Optics Light collection a) Larger Objective Deformation (Computer- Collecting Power Grows with Under Gravity controlled !!!!!!!!!Diameter 2 Mirror Shape) Objective Space b) Longer Motion of the Observation Time Earth

a) Increase Magnification Resolution Active Optics Air Turbulence = Focal LengthObjective Focal Length Eyepiece b) Reduce Diffraction: -> Larger Objective Space ≈ Wavelength Diameter Objective

a) Light gathering: - the larger the objective, the better: scales with area (diameter(objective)2) b) Magnification of image (apparent (angular) size ∆Q of object): ∆Qeye/∆Qobj = fobjective/feyepiece (f = focal length of the lenses) c) Resolution of neighboring objects the larger the objective the better: (objective >>>> wavelength!) The Limitation is diffraction Narrow slit does not produce a sharp slit image: a new wave starts at an obstacle when hit by a light wave and is bent around (like the circular waves starting from a stick in the water, when hit by a wave) D) Problems and Limitations: a) Lense errors chromatic aberration (due to dispersion) -> use mirrors (reflector telescope) other aberrations -> use correcting lenses b) Support of weight of the objective 32 -> distortion of mirrors or lenses by gravity ways out: -> make individual pieces (controlled by a computer) -> go into space (weightless) c) Motion of the air above observatory -> blurred image ways out: -> go on high mountains -> go into space -> use computer-controlled optics

33 3. Light is Electromagnetic Waves and/or Particles A) Spectrum of Light a) Dispersion refraction for blue light stronger than for red light -> prism produces "rainbow" Consequences: White light consists of all colors Frequency or wavelength ﬁ "color" Definition: Spectrum of light: the amount of energy at each wavelength b) Selective Reflection (produces colors) Colored object reflects only its own colors: -> selective reflection on solid surfaces -> info on material on planets/moons red surface of Mars -> rusty iron yellowish parts of Io -> sulfur c) Temperature (produces colors) Hot objects emit light: color (wavelength) of maximum intensity depends on temperature -> color of star -> info on temperature of star hotter -> blue -> shorter wavelength and hotter -> shines brighter There is "light" even beyond red (infra red) and beyond blue and violet (ultra violet) C) Light is Electromagnetic Waves Radio and TV transmission waves are similar -> electromagnetic waves (all the same "stuff", only at different wavelength) radio microwave IR red blue UV X gamma. low frequency high frequency long wavelength short wavelength low energy photons high energy photons For all: speed = c (the speed of light) (All electromagnetic radiation moves at c) D) Light is Particles Some measurements tell us light is particles (particle nature = "photons"). (electrons are knocked off by light, as if hit by a particle) -> light is particles -> light acts like both: waves and particles Frequency or wavelength equivalent to photon energy and equivalent to "color"

34 4. Radio telescopes A) Uses in astronomy all stars also emit radio waves (the sun is very noisy) gas (cold stuff) radiates in radio regime remainders of supernovae emit radio waves developed as spin-off of radar technology B) Radio telescope consists of antenna dish (collector for radio waves) and receiver (radio) (like satellite TV communication) C) Powers Signal collection: the larger the dish the better Resolution: dish larger than optical telescopes, but wavelength much longer! -> resolution worse than optical telescopes But telescope can be put together in pieces: With radio telescopes all over the Earth -> fake telescope as large as the Earth -> resolution better than optical telescopes

Penetration of Radiation into the Atmosphere Height in km 300 Satellites Visible

X-Rays 200 Radio

Gamma Rays UV Infrared

100 Balloons Planes

1 nm 1 µm 1 mm 1 m 1 km

-12 -9 -6 -3 0 3 10 10 10 10 10 10 m Wavelength

Radiation from the Stars

35 5. Space Astronomy A) The atmosphere blocks radiation only visible light and radio waves reach the Earth's surface (absorption by atmosphere, otherwise get fried by UV and X-rays) -> observe rest of spectrum from space B) IR light: - telescopes similar to optical telescopes - uses -> observe cool stars, star formation

C) UV light: - telescopes similar to optical telescopes - uses -> observe hot stars, local interstellar gas D) X-rays a) How to Image with X-rays? wavelength ≈ atom size -> mirror not smooth any more but rough surface looks shiny under flat angle -> Wolter telescope X-ray telescopes are world champions in mechanical accuracy (Guinness Book) X-RayX-Ray TelescopeTelescope

Wolter telescope

detector parabolic mirror in grazing incidence

small area nested mirrors for light collection Satellites: Einstein and ROSAT

b) Which eyes do we use for X-Rays? array of Geiger counters

36 c) Uses in astronomy - observe violent processes, star death - normal stars (like sun) when active - supernova remnants - galaxies and clusters of galaxies (very hot gas) E) Gamma-rays a) How to Image with gamma rays? use collision geometry of photons with electrons to get arrival direction (as if playing billiard with electrons and photons) (Compton Telescope, built at UNH and MPE) ComptonCompton TelescopeTelescope

Location of Origin in the Sky Photon Deflection Angle

Electron

Detectors

"Billiards" with Photons and Electrons

Detectors

b) uses - hottest and most energetic sites in the universe - black holes - active galaxies 37 F) Particles from celestial objects We can collect some samples of cosmic material in space, determine its composition and what gave the particles energy. a) Parameters to determine: Mass (M) -> composition, i.e, source of particles (oxygen from Earth, Helium from Sun) Energy (E) -> acceleration, heating best particle accelerators are in space Charge (Q) -> temperature at origin hot: -> atoms loose many electrons Combine several methods to achieve this: example: Deflection in electric field -> stronger for higher Charge (Q) Measure time-of-flight -> heavier (higher mass (M)) is slower Detector -> more energy (E) -> larger signal Bring instruments beyond Earth's atmosphere near Earth, near other planets, rest of the solar system b) Which samples of particles do we find in space? • cosmic rays (energetic particles) from the sun and other places in the galaxy • solar wind from the sun • interstellar gas from space outside the solar system • plasmas around planets (magnetospheres) • dust particles and meteorites To get samples from the Sun the surrounding interstellar gas and the cosmic rays from our galaxy is the Goal of the Advanced Composition Explorer (ACE)

38 VI. The Earth and the Planets 1. Magnetospheres A) The Earth is a magnet (magnetic compass) a) "Magnetosphere": It is a cavity in the solar wind and Contains Earth's magnetism Contains plasma from Earth’s atmosphere and solar wind Plasma: Gas with free electrons and ions. 99% of universe is plasma (reason we study plasmas in the solar system). Ion: Atom with some electrons knocked off by UV or collision with electrons Plasma is electrically conductive and can be trapped in magnetic field, because:

helical electron path

magnetic line

charged particles only move freely along magnetic field lines, but are forced into circles around the field lines. Key regions in the magnetosphere: b) Van Allen radiation belts (1958): charged particles spiraling on earth's magnetic lines. c) The solar wind produces a "geomagnetic tail" -- points away from sun. Corona changes fi solar wind changes fi magnetosphere changes Leads to magnetic reconnection in tail and on front reconnected field lines behave like extended rubber band -> can accelerate charged particles (electrons and ions) d) The Aurora Reconnection fi high energy electrons which spiral down magnetic lines fi hit upper atmosphere in polar regions fi light Auroral analogy: a big TV screen in the sky Auroral ovals: N & S hemispheres, around the magnetic poles Aurora not likely directly at the N and S geographic poles B) Other planets have magnetospheres. Jupiter's magnetosphere is the largest "object" in solar system Saturn, Uranus, Neptune have magnetospheres

39 MagneticMagnetic ReconnectionReconnection 1)1)

Magnetic Field Lines

2)2)

40 2. Planetary Magnetic Fields A) Earth's Magnetism Possibilities: Permanent magnet Current flowing through coil -> must be current, since magnetism is destroyed above 1000 C Convection of liquid iron in Earth's core and Rotation of Earth -> magnetic field B) Solid Earth (Interior) Only ≈ 2/1000 towards the center is known through drilling a) Density of Earth is 5 * water, but for rocks only 3 * water -> heavier stuff in interior (iron) b) Seismology Earthquake ﬁ compressional (P) waves (like sound) ﬁ shear (S) waves (like wave on string) P waves go through solid and liquid (you can hear underwater). S waves go through solid only. We deduce that the earth has a liquid core: P and S

solid

earthquake liquid

P only

Resulting picture of the Earth’s interior with 3 layers: Crust < 100 km rocks solid Mantle < 2900 km rocks solid Core rest very heavy; Fe, Ni liquid c) Hot interior from radioactivity radioactive decay heats up the interior of the Earth (nuclear waste needs to be cooled for long time) d) Convection: hot stuff rises and cool stuff sinks (analogy: pan of water on a hot stove) Results: -> magnetism -> formation of surface structures (volcanoes, plate motion)

41 C) Magnetism on Other Planets Provides information about their interiors In analogy to Earth they need: Electrically conducting substance and Motion (rotation and/or convection) in interior a) Inner Planets Earth: Molten iron core and Rotation Heat ﬁ convection -> magnetism. Venus: Molten iron core (evidence: dense; active volcanoes) but very slow rotation -> no magnetism. Mercury: Iron core (evidence: dense) May not be molten (evidence: no heat flow from interior) Very slow rotation but here is weak magnetism -- a riddle Mars: No liquid iron core (evidence: low density, iron in surface, no active volcanoes) Very weak magnetism in spite of fast rotation as Earth.

Planetary Magnetic Fields

Earth Venus Mercury Mars Moon

Weak Magnetic Yes No No No Field (Riddle)

Liquid Iron Yes Yes Iron No No Core but solid

Rotation 24 hours 240 days 58 days 24.5 hours 28 days Period

42 b) Outer Planets Composition of giant planets: like Sun (75% H, 23% He, rest heavy elements) But interior: compressed that H is metallic (in Jupiter and Saturn)

Jupiter Saturn Uranus Neptune

Magnetic Field Yes Yes Yes, off Center Yes, off Center Strange Direction Strange Direction

Hot Liquid Interior Yes Yes Yes Yes Metallic H Metallic Hydrogen Water Water

Rotation ≈10 hours ≈ 10 hours ≈ 17 hours ≈ 16 hours

Other planets (except Pluto)

Orbital planes

Sun Uranus (screwy rotation, Neptune screwy magnetism) (normal rotation, screwy magnetism)

43 3. Surface of Planets and Moons A) Plate tectonics Coast lines of continents (Africa and America) fit together Motion of continents (2 - 4 cm/year) Convection fi continental drift fi Earth's early history has been erased So we look at other planets, moons, asteroids, and comets to learn about the early solar system. Venus and Mars have no sign of plate motion B) Volcanism on planets: They are the result of hot interior of planets due to radioactivity They occur at "hot spots". Continental drift carries earth's surface over the hot spots fi chains of small volcanoes.

look around -> Mars: dead volcanoes Venus: active volcanoes (evidence: we detect volcanic gases in Venus' atmosphere) Mars and Venus have no continental drift. Volcanoes sit over hot spots ﬁ huge volcanoes

C) Volcanism on moons a) Tidal volcanism Io shows volcanism Tidal flexing (from passage of next moon) + internal friction ﬁ heating. (Different from volcanoes on Earth: from radioactive heating!) Hot enough to melt sulfur Similar effects on other moons: Water geysers (?) on Saturn's moon Enceladus and Jupiter's Europa ﬁ snow and bright surface. Tidal flexing enough to heat water. b) Sun driven volcanism: Ice geysers on Neptune's moon Triton. sun-driven liquid nitrogen volcanoes (?) Comets in the inner solar system: ejection of material sun-driven ejection

44 D) Craters on Moon and Mercury Many craters on the surface -> no change by weather as on Earth -> no atmosphere Possible reason for craters on the moon and Mercury? Volcanoes? no evidence, not the right conditions Impacts? yes, lots of debris in the solar system a) Crater size depends on energy of object, not on its size b) Most craters found throughout the solar system are the remains of the last objects to fall onto the planets or moons during formation bombardment up to 3 billion years ago (evidence: dating of lunar rocks) Earth has few visible craters because of - plate tectonics (renewal of surface) - weathering E) Age of formations a) Age Determined from rocks sampled by Apollo astronauts oldest rocks ≈ 4.5 billion years b) Method: radioactive decay e.g., Thorium -> several steps -> lead ratio of lead/thorium is measured -> age F) Formation of the Moon

a) Earth and Moon Formed Together Twin Model Problem: Density of the Moon < Density of the Earth -> Not Formed from Same Material b) Moon Captured by the Earth Spouse Model Problem: Object approaching planet from far away does not orbit without deceleration -> Cannot Be Captured c) Moon Ejected from Earth After Impact Child Model Evidence: Density = Earth's Mantle Composition = Earth's Mantle Moon contains few volatile materials (water, gases) fi heating during impact? Big impact fi other early moons fi collide with each other fi debris fi collide with the Moon fi Moon's craters(?) -> Current Best Model Speculation: The impact, which formed the moon, may have removed earth's early CO2 atmosphere. This may be why we are not like Venus.

45 4. Planetary Atmospheres A) Existence of atmospheres high temperature -> gas molecules faster -> escape easier larger planet -> stronger gravity -> keep gases around planet Mercury: hot and small -> no atmosphere Moon: small -> no atmosphere B) Greenhouse effect: a) selective absorption of light

29% of IR Atmosphere absorbs 71% of IR and warms up. Sunlight IR

Earth absorbs most of the sunlight and radiates IR.

b) Greenhouse gases: Water vapor (deserts get cold at night). Early earth: water vapor ﬁ strong greenhouse. Carbon dioxide (CO2). Methane (not much methane but a very strong absorber).

c.f. Venus: CO2 atmosphere fi strong greenhouse fi hellish place (>480 C) Mars: Thin CO2 atmosphere. (cold) Venus, Mars have CO2 fi Earth probably started with lots of CO2 Where did Earth's CO2 go? i. Water dissolves CO2 (e.g. soda pop). Water + CO2 fi carbonic acid. Carbonic acid + Calcium or Magnesium salts (washed into ocean by rivers) fi precipitated carbonates fi settle to bottom of ocean fi limestone (calcium carbonate) and magnesite (magnesium carbonate) sedimentary rocks. ii. Life stored CO2. e.g. chalk or oil and coal deposits iii. Volcanoes release the CO2 stored in rocks fi cycle Importance of volcanoes: Add CO2 and water to atmosphere fi greenhouse Thus recycle CO2 from buried carbonate rocks May have happened in the past on Mars, but not recently

46 5. Water on Planets Mercury too hot and no atmosphere Venus too hot -> water vapor -> destroyed by intense solar UV Water on Earth important for life -> What about Mars? A) White polar caps which show seasons -> dry ice (CO2), cannot be pure water (atmospheric pressure too low) B) Mars canals were reported (Schiaparelli, last century) only seen with human eye, not on photographs (the eye/brain connects uncorrelated dots) But more recently riverbeds found fi Mars had liquid water (evidence: riverbeds) fi thick atmosphere in past Where did Mars' water go? Low pressure atmosphere fi water cannot exist as liquid (c.f. 'dry' ice is left in polar caps) fi water vapor broken up by solar UV or buried by permafrost 6. Conditions for Life • reasonable temperature: presumably 0 C < temperature < 100 C • atmosphere with reacting gases: O, N, CO2, and/or methane • a liquid, in which life can thrive (on Earth: liquid water; anything else??) We may find surprises!!!

47 7. Ring Systems Saturn known for beautiful ring system but also found at Uranus, Neptune and Jupiter a) Why a ring and no moon? -> Tidal forces: Roche Limit is due to Competition between: Tides from planet ﬁ try to tear apart a moon Self-gravity ﬁ tries to hold moon together Inside the Roche Limit: tides win. Tides will overwhelm self-gravity and tear apart a moon inside the Roche Limit. This will happen to Neptune's Triton when it comes closer to the planet! Or tides will prevent a moon from forming inside this distance Almost all rings are inside the Roche limit. (Saturn, Jupiter, Uranus) b) Why are the rings so stable and sharply structured? It's all gravitational interaction! Shepherd satellites "focus" skinny rings, which would be expected to "diffuse"

slow moon reduces ring particles' energies

ring particles have intermediate speeds

fast moon increases ring particles' energies

Sharp edge of Saturn's A ring: small moon just beyond the ring Encke division in Saturn's A ring: small moon slinging particles out of the division

48 8. Small bodies in the solar system A) Asteroids Fill large gap between Mars and Jupiter Asteroid belt: a small planet which couldn't come together because of Jupiter's gravity. B) Comets a) have very eccentric orbits -> come from freezer into warm sun -> evaporation b) have 2 tails dust tail -> comet dust -> driven by radiation pressure of the sun plasma tail -> gas from comet gets ionized by UV light of the sun -> blown by solar wind (first recognition of solar wind (Biermann, 1949) investigated by active experiments (artificial comets) c) comet is dirty snowball (fluffy configuration) (Whipple) but under bombardment from solar wind and cosmic rays -> tar-like substance on surface -> very dark surface (observed by the Giotto spacecraft) -> material comes out in bright geysers d) come from Oort Cloud of comets -- way beyond Pluto. Comet orbits suggest a huge reservoir of objects far away. However, they could not have formed there, wasn't enough material out there. They probably formed near U and N and got ejected by a slingshot by J, S, U, N C) Meteors Provided the only hands-on material for a long time Debris of the solar system fi hit Earth's atmosphere ("meteors") fi called "meteorites" if they land There are three types of meteors: Carbonaceous, stony, iron a) Break-up comets - Meteor showers along comet orbit - Fluffy structure like comets, break-up of comets observed Carbonaceous chondrites contain volatiles fi no differentiation fi sample of early solar system like comets.

b) From asteroid belt Asteroids collide ﬁ small debris ("meteoroids") Iron and Stony meteorites ﬁ some asteroids were big enough for differentiation.

c) Impacts and life:

i ) Carbonaceous chondrites contain water & complex molecules including amino acids ﬁ building blocks of life were there at the beginning of the solar system. Comets and water-bearing asteroids may have been early sources of water and building blocks of life.

49 ii) Major extinction of life 65 million years ago. - Dust or CO2 , from an impact: change of climate ? killed dinosaurs and other life forms? Evidence: Iridium is very rare on Earth (likes to be with iron so most of it probably sunk to the Earth's iron core). Iridium is much more abundant in iron meteorites. 1980: Luis (Nobel prize for something else) and Walter Alvarez found a 65 million year old layer of rock with a lot of iridium. Conclusion: fi the iridium came from space. Amount of iridium fi the object must have been 10 km across fi it would have made a crater 150-200 km in diameter. A crater of the right age and size (≈ 300 km) has been found in Yucatan. Alternate theories: - lots of volcanoes changed climate - radiation from nearby supernova killed life Riddle: Life began 3.8 billion years ago. But there was intense bombardment up to 3 billion years ago fi dark dusty sky and boiling of oceans. How did life start under these conditions?

50 9. General Features of Planets A) Orbits Almost in the same plane Almost everything has same sense of spin B) Appearance and composition Close to sun: rocky planets and rocky debris Far from sun: gaseous planets, icy satellites, icy debris (comets) Exception: Pluto and Charon are ice + rock -- a riddle Did they get knocked out of Neptune's system of moons? Are there lots of Plutos out there?

Close to sun: "volatile" stuff evaporated ﬁ "refractory" stuff remains Far from sun: cold ﬁ even gases could accumulate without escaping gravity Result: giant gaseous planets J,S,U,N far from sun C) Similarities in Jupiter's system: Close to Jupiter: Io and Europa are rocky Far from Jupiter: Ganymede and Callisto are ice + rock Conclusion: Jupiter produced heat (from gravitational energy) while it formed To be explained by model on solar system formation!

51 VII. Observation of the Sun and the Stars

We start with our sun as an example: • Energy source of our solar system • Sun is a typical star -> good example for all other stars The material for the many stars needs to be organized.

1. Luminosity, Distance, Size A) Magnitudes etc. First and most obvious parameter: How bright is the star in the sky? old classification according to sensitivity of the eye Bright 1 ..... 2 ...... 3 ...... 5 ...... 6 Faint (higher value of magnitude means fainter) Brighter can mean -> more luminous and/or -> closer to us Ergo: We need the Distance! B) Distances: Sun: r = 150 Mio km derived through Kepler's 3rd law and parallax to other planets Stars: parallax with the orbit of the Earth as baseline (largest baseline possible) very skinny triangle (works up to ≈ 100 parsec) C) Size: Sun: d = 1.39 Mio km derived from angular size (skinny triangle) Stars appear as points, even in largest telescopes D) Luminosity Energy flux (sun): L = 4*1026 Watt Derived from energy flowing through 1 m2 at the distance of the Earth ≈ 1400 Watt/m2 (solar constant) and multiplied by the surface of the sphere at the distance of the Earth Total energy radiated on Earth is > 10000 times the energy used by mankind!! -> may be enough for our energy demands Our energy usage must remain at tiny fraction of the solar energy flux! Artificial production of only 1.3% of the solar energy flux -> 1o C temperature increase on Earth radiation balance (as discussed for sun below) Stars: L = total energy emitted by the star (derived from magnitude and distance: parallax). Magnitude (or Brightness) scales like Luminosity*1/Distance2

52 2. Spectroscopic Measurements A) Temperature: Sun: T = 5500 K derived from solar radiation Sun is the best "black body" in the solar system ﬁ photons have many collisions with matter before escaping ﬁ photons "know" about temperature Black Bodies: stars, planets, cloud tops, rocks in rings, dust particles Not Black Bodies: corona, nebulae (not dense) A “Blackbody” spectrum a) is peaked with a distinct maximum at a certain wavelength b) Its total radiation and distribution over wavelength depends only on T a) Wien's Law: temperature* wavelength(max) = constant Sun has maximum at green (our eyes work best for this color) -> T Hot stars: blue, UV. Sun: yellow. Cool stars: red. very cool stars: proto stars: dust heated by stars: IR. planets: cloud tops: -> We can get the temperature from the color or the wavelength with the maximum SpectraSpectra ofof DifferentDifferent TemperatureTemperature Wavelength x T = Constant (Wien's Law) T = 7250 K Maximum of Intensity T = 5500 K

T = 3625 K Intensity of Light

0 200 400 600 800 Wavelength in nm T x 2 Wavelength / 2

53 b) Stefan Boltzmann Law: energy flux = constant * T4 In words: higher energy flux -> means higher temperature of the star and a brighter star surface SpectraSpectra ofof DifferentDifferent TemperatureTemperature

4 Energy Flux x 16 Energy Flux = Constant x T (Stefan-Boltzmann)

T = 7250 K T x 2

T = 5500 K

T = 3625 K Intensity of Light Energy Flux of Light

0 200 400 600 800 Wavelength in nm

Application to the observation of stars: B) Size of stars get: From distance and magnitude combined ->Luminosity From Wien's Law -> Temperature Form Stefan-Boltzmann Law -> Energy Flux/area Combine Luminosity and Energy Flux/Area -> Surface of Star -> Diameter

54 C) Composition: Sun: 75% H, 23% He, 2% "metals" Derived from Fraunhofer lines in spectrum Each atom, ion, molecule absorbs or emits at its own set of frequencies. Reason: Electrons are confined to specific orbits in atoms (Bohr's Model of atoms <-> Quantum Mechanics)

emission line energy output

absorp. wavelength line

Absorption line: material in front of "black body" -> sun's atmosphere Emission line: thin material radiating -> outer atmosphere -> identify Nebulae = gas clouds = emission lines (not black body) Galaxies = sum of black bodies from many stars (plus the stars' absorption lines) Uses (for all stars): a) What's there? (H, He, etc.). Determined by specific set of lines: Hydrogen alpha line = red (most abundant element) (Hydrogen at 10,000K or near a star at 10,000K) e.g. chromosphere prominences -> red is the color of the universe! nebulae b) Abundances: Relative intensity of lines -> differences in composition The universe was born with H and He only (almost) Heavy elements were made in stars Population I: 75% H, 23% He, 2% heavy elements ("recycled" material ) Sun is Population I Population II: 77% H, 23% He, few heavy elements ("more primitive" material) Where are the true "ﬁrst" stars (H, He only)?

55 3. Stellar Mass and Density A) Solar Mass: M = 2*1030 kg derived from Kepler's 3rd law (planets) B) Binary Stars and Mass Determination Velocities can be measured with Doppler Effect: Spectral lines key to Doppler: (we know the frequencies when there is no motion) Velocity Away from us fi frequency decreases = redshift Velocity Toward us fi frequency increases = blueshift Velocity Across fi no shift 2 possible ways to get the star mass: 1) Doppler effect -> Velocity of stars + orbital period or 2) Distance of binary stars -> distance between 2 stars + orbital period use Kepler's 3rd law -> mass of stars

C) Density r: Sun: r = 1.4 g/cm3 combined from 2B) and 3A) 1.4 times density of water Red Giants: much less dense White Dwarfs: much denser Determination of the Star Parameters

Parameter Observation Deduction ______Apparent Magnitude Measure Brightness Distance Parallax Distance Luminosity Combine: Distance and Apparent Magnitude Surface Temperature Color of Star (Wien's Law) Spectral Lines Energy Flux/Area from Temperature (Stefan-Boltzmann) Size Combine: Luminosity Energy Flux/Area Composition Spectral Lines Elements Mass Distance or Velocity and Use Kepler's 3d Law Orbital Period of Binary Stars ______

56 4. Classification

According to their color stars have been organized in classes: blue yellow red O(hot) B A F G(sun) K M(cool). "Oh, Be A Fine Girl (or Guy) Kiss Me" A) H-R diagram. Essentially luminosity vs. temperature. Main sequence (distinct line filled with stars through the center diagonal) Red super giants, red giants (upper right). White dwarfs (lower left). Main sequence: most stars (90%) (stars spend most of their lives on main seq.) Main sequence: most stars are less massive than the sun because They burn fuel slowly and live a long time (the sun is not an average star). Main sequence: few O & B stars: they don't live long Few giants, supergiants: don't stay around long ("senility") White dwarfs (10%): "dead"

Larger mass Larger size Blue giants Very few stars Red supergiants Red giants

main sequence

Small mass sun Small size WD Red dwarfs

Luminosity Most stars

Temperature

a) Sizes: White Dwarfs hot (high energy flux density) and dim -> small Red Giants cool(low energy flux density) and bright -> huge b) Spectral Parallax: 2nd way of getting stellar distances Each point on the HR diagram has a spectral signature (lines). Use spectral lines to locate star on HR diagram. HR diagram ﬁ luminosity Luminosity & apparent brightness ﬁ distance

c) Variable stars (e.g. Cepheids) Variation period increases with luminosity 3rd method to determine stellar distances Cepheids used as huge standard candles

57 Determination of Star Distances Method (Range) Observations How to do? ______Geometric Parallax Measure star position Use diameter of Earth's orbit (≈100 Parsec) 6 months apart as baseline! -> angle and Earth's orbit lead to distance (like distance of the moon or planets)

Spectroscopic Measure temperature Find position of star in HR Parallax of star diagram -> get luminosity (≈20,000 Parsec) and apparent e -> o sity and magnitude lead to distance

Cepheid Variables Measure period Period determines of variable luminosity (≈20 million Parsec) and apparent magnitude -> luminosity and magnitude lead to distance ______

B) Mass Luminosity Relation Luminosity of stars varies like Mass * Mass * Mass * √Mass But: Total amount of Fuel of the Sun scales like Mass The poor are saving and the rich are squandering -> more massive stars die faster, because they run out of fuel faster!

58 VIII. Understanding the Sun Our Star 1. Interior of the sun (Deduced from measured parameters) A) Energy source Need to sustain ≈ 4 x 1026 Watt = luminosity (for > 4.5 billion years!) Possibilities that have been discussed are: a) Sun of pure coal and oxygen Life of ≈ 10000 years -> much too short b) Shrinkage under gravity -> increase pressure -> increase T -> radiate energy Life of ≈ a few million years -> too short TheThe EnergyEnergy SourceSource ofof thethe SunSun Factoid: The sun is already 4.5 billion years old

Source How? How Long? Adequate? Chemical Reaction (Burning) Coal + O O 10,000 Years No Oxygen C + C + Heat O O

Sun shrinks Pressure increases Gravity 10 Million Years No Heat is produced

Nuclear Fusion 4 H -> He + 2 Positrons + g Photons + Neutrinos Hydrogen 10 Billion Years Yes Nuclei He weighs less than 4H E = M x c 2

59 NuclearNuclear FusionFusion EnergyEnergy onon thethe SunSun

4 x 1 Proton He = 2 Protons 4 H + 2 Neutrons weighs less!! (0.7%)

Einstein: Energy = Mass x (Speed of Light)2 E = M c2

Mass is converted to Energy!!

But: Protons Repel each other by Electric Forces

Only if the energy is high enough: + + + + Neutrino g e

1 2 2 1 H -> 1 H + Positron + Neutrino + Gamma 2 x

2 1 3 2 x 1H + 1 H -> 2 He + Gamma Number of Nucleons 3 3 4 1 2He + 2 He -> 2 He + 2 1 H Number of Protons

60 c) Nuclear Fusion (Bethe: Nobel Prize) 4H ﬁ He + gamma photons + neutrinos stay in sun escape (collide with matter) (interact very weakly with matter) He has less mass than 4 H atoms, and the 'mass difference' is converted into energy via E = m c2 (Einstein) The energy appears as gamma photons and neutrinos. Fusion requires high temperature to overcome electric repulsion between positively charged nuclei ("fusion ignition temperature"). Fusion requires high density for lots of collisions. Thus Fusion occurs only in a small central 'core'. (T ≈ 15 million K) On Earth so far only used in Hydrogen Bombs (ignited by a nuclear bomb) nuclear fusion reactor difficult -> hot stuff flies apart too fast try: magnetic containment Why does the sun not explode like a nuclear bomb? the sun has a built-in safety valve and thermostat: more fusion -> T increases -> pressure increases -> sun expands -> T decreases -> less fusion ThermostatThermostat inin StarsStars

Pressure Increased

Core Expands Too Much Fusion Density Reduced -> Core Too Hot -> Less Fusion Reactions

Core is Cooling The Energy Output is Stabilized! Pressure Reduced Density Increased -> More Fusion Reactions

61 B) Hydrostatic equilibrium Pressure = weight of overlying stuff (Competition: Pressure and Gravity) Pressure increases inwards. since: Density increases inwards (more dense sinks) and Temperature increases inwards (to carry energy outwards) gas under pressure gets heated (as pump for bicycle) C) Information from the interior a) Neutrinos: Detection = proof of fusion They have no mass[?] but energy -> One "view" of sun's interior can pass through matter not electromagnetic radiation "Solar Neutrino Problem": only 1/3 of expected flux detected Possible explanations (?): - Detector problems? checked with other detectors - Nuclear data incorrect? checked with accelerators - Model of sun incorrect? only one side reaction checked -> get neutrinos from pp reaction - Neutrinos change on way -> neutrinos would have small mass and/or interact with sun's magnetism All stars make neutrinos -> universe full of neutrinos Can neutrinos with mass solve the missing mass problem? GALLEX experiment: main reaction neutrinos react with Gallium -> supports low values -> neutrino mass very small -> but strong indication that neutrinos change identity on the way to us Neutrino identity change recently confirmed as the main reason for the puzzle Neutrinos have mass! b) Helioseismology (like earthquakes) Doppler effect ﬁ Surface moves up and down (like the ocean) Period about 5 minutes "5 minute oscillations" Sound waves trapped inside sun Our 2nd "view" of sun's interior Results: Provide insight into energy transport and rotation Do not solve riddle of magnetic field generation -> extended measurements with SOHO and GONG D) Energy transport to surface a) Energy flow by photons: Requires temperature decreases outwards Photons have many collisions with matter on way out Their energies "degrade" on way out: gamma -> X -> UV -> visible b) Energy flow by convection (outer shell) - Hot rises - Cool descends More efficient than photon transport in outer shell of sun

62 2. Solar atmosphere A) Photosphere: a) Definition: Where energy (visible light) comes from b) Structure: Granulation - All over sun (except in sunspots) - Small scale convection on surface (like boiling teapot) Velocities can be measured with Doppler effect: c) Activity Sunspots darker -> lower temperature Energy transport choked off by magnetic field Zeeman splitting of spectral lines fi magnetism measured Sunspots: strong magnetism. Sunspots with complex magnetism fi flares Sunspots have 11 year cycle + other changes. Fewer sunspots fi fewer faculae fi sun dimmer fi colder climate (no sunspots in 17th century) fi 'little ice age'

Alternate view: dust from volcanoes made the little ice age and other cool periods. B) Chromosphere: Somewhat hotter and thinner above coolest layer of sun ﬁ heating by magnetic fields (wildly stirring in the atmosphere) Here prominences are observed (more material than in neighborhood) red prominences

sun

red chromosphere Hydrogen at 104 K ﬁ red emission.

Chromosphere: thin layer below corona Prominences: chromospheric material held up by magnetism (in dilute corona)

Prominence supported by magnetic tension

Kinked magnetic lines

63 C) Corona: a) Hottest and outer part of solar atmosphere Temperature = 1 - 3 million degrees K Deduced from highly ionized iron in the corona Coronal heating - a riddle [Sun's surface = 5800K; corona = few million; but heat likes to flow from hot to cold] Current best model: Combination of motion and magnetism (strong heating where strong magnetism) -> Magnetic energy is converted to heat energy b) Corona is structured by magnetism: Lines and loops Due to: electrons spiraling around magnetic lines

helical electron path

magnetic line

Magnetic lines are like taut strings i. Waves carry energy (Alfvén waves - Nobel prize) ﬁ heat ii. Magnetic reconnection turns magnetic energy into motion (kinetic energy)

oppositely directed reconnected magnetic magnetic lines are kinked lines

jets, heating, energetic particles

64 D) Solar Wind a) The corona overcomes solar gravity Solar Wind: regions of the corona flow out to Earth and beyond Strong solar wind originates over poles of the sun: Goal of Ulysses (over solar poles in 1995/96) Competition Gravity and magnetism hold atmosphere down Temperature escape ﬁ solar wind Solar wind flows with supersonic speed When it runs into obstacles (Earth’s, other planets’ magnetic field), it forms a Bow Shock = “Supersonic Boom of the Earth in space” b) Solar wind carries sun's magnetism To Earth and beyond Sun's magnetism + Earth's magnetism ﬁ aurora etc.

c) The corona and solar wind change ﬁ affects Earth

i. Solar cycle (number of sunspots) ii. Coronal transients (coronal mass ejections) ﬁ ejection of plasma and magnetism

d) Shield against cosmic rays The solar wind makes it hard for other plasmas and charged particles to move in -> first shield against cosmic rays for the Earth Altogether there is a 3 layer shield around Earth: i. Solar wind (sun's magnetic field) ii. Earth's magnetic field iii. Earth's atmosphere

65 IX. What is between the Stars? 1. Boundary of the solar system Solar wind is stopped by interstellar gas and plasma -> Decelerated to sub-sonic speed -> Heliospheric termination shock Ions accelerated at the shock: like playing Ping Pong between the two sides MultipleMultiple ReflectionReflection UpstreamUpstream andand DownstreamDownstream ofof thethe ShockShock

Shock Plane

== FermiFermi AccelerationAcceleration

66 2. Interstellar gas in the solar system a) Neutral gas enters the solar system from outside InteractionInteraction ofof InterstellarInterstellar GasGas withwith thethe HeliosphereHeliosphere

Interstellar Neutral Gas Flow Heliosphere

Solar Wind

Magnetic Field

Shock

Heliopause

b) Neutral gas is ionized Close to the sun by UV radiation Impact of solar wind ions Impact of solar wind electrons

67 c) New ions will feel the magnetic field which is imbedded in the solar wind -> ions gyrate around magnetic (Giant Swing around field line) -> ions will be swept out of the system These ions have been measured! -> local information about the gas outside the solar system (interstellar gas) d) Sun moves with respect to the gas -> Interstellar wind (like wind felt in a cabrio) Sun acts as gravitational lens -> gas focused on the downwind side Measure Determine absolute ion flux -> density density enhancement in focus -> velocity and temperature of interstellar gas

68 3. Gas Between the Stars a) Absorbs light from stars Observe dark lines in star spectra. Interstellar gas is distinguished from stars through the Doppler effect (different motion). b) Emits light When in the vicinity of bright stars -> observe emission lines c) Cold gas emits radio lines 21 cm line of un-ionized Hydrogen Importance: lots of hydrogen in the universe; Spectral line ﬁ get velocity with Doppler effect Radio line ﬁ can see through dust (see below)

Molecules: Cool clouds fi molecules don't break apart when they collide Dense clouds fi better chance for atoms to form molecules Cool and Dense fi Molecular clouds are "stellar nurseries"

69 4. Dust Between the Stars a) Light scattering:

incoming photon small particle

scattered photon

b) Obstruction (extinction). With light, we can't see very far into the Milky Way c) Reddening: Red light goes through, blue is scattered blue

"white" light

dust cloud red, IR, radio star*

blue

-> Radio & IR astronomy: see through dust clouds d) Blue reflection nebulae - Blue scattered light to the side

Same physics in Earth's atmosphere ﬁ sunsets are red "Alpenglow"; sky is blue

Alpenglow see red sunsets sunlight

see blue sky

70 e) Why is there dust? Cool clouds ﬁ dust doesn't evaporate Dense clouds ﬁ more chance for molecules to come together

71 X Stellar Evolution 1. Star formation A) Conditions for star formation Cool fi temperature can't overwhelm gravity Dense fi more self gravity Cool and Dense fi Molecular clouds with dust are "stellar nurseries" Dust serves as a "cooler" for the gas to make collapse possible But: Need IR or radio to see through dust into star-forming regions B) Start of the collapse clouds need to be a little denser to collapse fi trigger shock wave, for example from a supernova can push gas together C) Role of dust in star formation: As a cloud collapses it heats up (compression heats) fi temperature resists gravity fi it would stop collapsing The dust can radiate the heat, keep cloud cool enough to continue collapsing

Trigger of Star Formation

Shock Wave Interstellar Gas Cloud

Shock Wave

72 2. Formation of the solar system and other Planetary Systems A) Solar System Models Conservation of angular momentum fi collapsing cloud rotates faster fi it would stop collapsing fi most of angular momentum in planets Still not enough fi angular momentum problem Loss of angular momentum -> solar wind -> magnetic field Both carry angular momentum away CollapseCollapse ofof RotatingRotating CloudCloud

Gravity

Centrifugal Force

Interstellar Gas Cloud

73 B. Planets in Other Star Systems a) Detection Techniques Motion of the star in response to the planet’s gravitational pull - transverse motion in the sky - motion away or towards us (Doppler effect) Plan to build huge telescope clusters in space to see these planets b) Types of Planetary Systems Planets of pulsars (probably not from star formation) Jupiter-size planets close to the star Jupiter-size planets further away (similar to our solar system) Greater than Jupiter-size planets in eccentric orbits (more like binary stars) This is just the beginning, the heavy ones are the easiest to find. c) Consequences of the Findings -> planetary systems probably a general feature of stars -> possibly many, many planetary systems in the universe -> opens many chances for life to emerge! -> planetary systems may be more diverse than our solar system

74 3. Mature stars A) Range of stars Masses 0.1 to 60 solar masses Luminosities 10-3 to 106 solar luminosities Smaller fi not enough central pressure to ignite Fusion Brown Dwarfs may contribute to dark matter in universe Larger fi higher radiation pressure than gravity Fly apart Eddington Limit of stars B) Basic model of stars (like sun) Interior: pressure, density, temperature increase inwards but gravity balanced by pressure from hot (burning) core maintains burn rate fi star's thermostat

More massive star fi higher central pressure fi hotter, denser fi more fusion fi more luminosity fi fuel used faster fi shorter life

a) H core "burns" first = Main Sequence: Star on main sequence for long time (lots of hydrogen) ThermostatThermostat inin AgingAging StarsStars

Pressure too Low

Core Compressed

H fuel partially used Density and Temperature -> Less Fusion Reactions Increased -> Core Cools -> More Fusion Reactions -> Pressure too Low The Energy Output Core is Hotter is Stabilized on a Higher Level!

Radiates More Energy 4 Thermostat is set (Increased with Temperature ) higher!!!

75 b) Core compression: Pressure goes as (particles per volume) x temperature Fusion removes particles with time fi Volume must decrease (compression) fi temperature and density increase fi more fusion fi more luminosity

"Early Sun Paradox": the sun was much dimmer when life began Possible answer(?): more carbon dioxide ﬁ stronger greenhouse effect ﬁ helped keep early Earth warm

76 4. Aging of stars a) He core (no fusion), H-"burning" shell He core shrinks to maintain pressure and drags down overlying H Overlying H starts "burning" on an overheated oven Luminosity increases: ﬁ red giant Surface expands and cools ﬁ red

4b Red Giant 4a

3Bb

3Ba

Luminosity HR diagram Temperature

b) Degenerate He core Electrons can't be packed closer fi (huge) "Degeneracy Pressure" rising temperature does not increase pressure fi thermostat does not work fi He fuses in flash then a lot of heat overcomes problem

c) He core fusion ﬁ C, O Core expands and shell "burning" less important Luminosity decreases ﬁ Surface shrinks and warms up

d) C, O core He core burnt out ﬁ He shell burning (similar to 2a)

e) Heavy elements made up to Fe (Fowler: Nobel Prize) But: Heavier than Fe requires energy Fe nucleus + (something) ﬁ more mass than sum of parts Requires energy to be converted into mass; from gravity

77 f.) No more fuel Radiation balanced by loss of gravitational energy ﬁ contraction ﬁ hotter But: only up to when the electrons cannot compressed any further Degeneracy Pressure as under 2b Tests of the star model - Temp - luminosity relation (the HR diagram) - Mass-luminosity relation - Abundance of heavy elements - Star Tracks (clusters = same age stars)

4f 4e 4d 4b Red Giant 4c 4a

3Bb

3Ba 5Aa

Luminosity HR diagram Temperature

78 5. Star deaths A) Low mass stars a) White Dwarf is their corpse Electrons can't be packed too close together fi "electron degeneracy" fi huge pressure White Dwarf supported by electron degeneracy pressure M < 1.4 Msun (Chandrasekhar: Nobel Prize) b) Mass loss via stellar winds and/or pulsed ejection fi planetary nebulae fi recycling Star reduces mass to 1.4 Msun limit B) Binary Stars a) Novae: An example of mass transfer in a binary star system White Dwarf gains mass (Hydrogen) from other star fi explosive (degeneracy) fusion on surface (high temp & pressure)

b) Type I Supernova An example of mass transfer in a binary star system White Dwarf + more mass fi shrinks fi hotter interior Collapse when M >1.4 MS fi sudden flash of fusion (very rapid due to degeneracy) fi White Dwarf explodes fi recycling Type I Supernovae have all the same luminosity fi excellent bright Standard Candle

C) High mass stars a) Type II Supernova Process Heavy star with degenerate iron core (no more fuel) (see 2f) Fe core gains mass from overlying layers to > 1.4 Msun fi electron degeneracy pressure fails fi collapse fi neutron star core or black hole core 'Rebound' of falling material on core and neutrinos from core fi expulsion of outer 80% of star Energy source = gravity

79 Type II Supernova Explosion

Star Layers With Si, Mg, Ne, O, C, He and H

Nuclear Explosion

Shock Wave

1. Collapse of Core 2. Outer Material Follows 3. Rebound at the Core, Shock Wave and Nuclear Explosion

Lots of neutrinos from collapse (Neutrino flash observed from SN1987) Theory ﬁ Type II SN's come from massive supergiants SN 1987: a massive supergiant disappeared

80 b) Consequences of SN Remnants: - Expanding hot nebula some only visible with X-ray telescopes, only now discovered - High-energy electrons (cosmic rays) - Neutron star or black hole Importance of SN's: i. Neutrino astronomy 1987 SN: neutrinos fi proof of neutron star formation neutrinos arrived before light fi action was in the star's core all neutrinos arrived at same time fi upper limit on neutrino mass ii. Make elements heavier than Fe: Fe nucleus + (something) fi more mass than sum of parts Requires energy to be converted into mass; from gravity 1987 SN: gamma rays from radioactive cobalt fi proof of heavy element formation iii. Recycling of material (we are made of 'star stuff') iv. Produce shocks = denser, higher pressure gas v. Shocks initiate star formation "Life Cycle of Stars"

shock

high pressure gas SN cloud

Density increases ﬁ more self-gravity Solar system formation triggered?? vi. Shocks ﬁ cosmic rays via repeated bounces off converging "mirrors" like at shocks in the solar wind (see IX.1.) c) End products

Neutron star when M > 1.4 Msun e + p + squeeze ﬁ neutron + neutrino (most of SN energy) stable by Neutron degeneracy pressure if M < 3(?) Msun 1 sugarcube of Neutron star material = 1 billion tons (Mt. Washington)

Observation: Pulsars rapidly pulsating radio sources (Hewish: Nobel Prize) fi Rotating neutron stars with strong magnetism Analogy: a lighthouse Conservation of angular momentum fi rapid rotation after collapse Compression of magnetic lines fi strong magnetism Strong magnetism fi synchrotron radiation

81 Importance of pulsars: i. Prove neutron stars exist ii. Found in SN remnants: Prove Type II SN scenario iii. Energize SN remnants (e.g. synchrotron from Crab Nebula) Hypothesis: Rotational energy from the pulsar powers the Crab Nebula Prediction: The pulsar should gradually rotate more slowly Test: It slows down at just the right rate iv. Tell us where SN's have occurred: Globular clusters have had Many SN's which may have ejected stars from the clusters v. Precise clocks in space: e.g. Doppler effect ﬁ the "new planet" around a pulsar e.g. used to study interstellar plasma

Signal Strength DetectionDetection ofof PulsarsPulsars Radio Pulse 0.001 sec

1.3 sec Time

late signal

early signal

Pulse Length Radius of Object

Radius

82 d) Binary X-ray sources: Examples of mass transfer Mass from normal star onto compact object fi compression fi Enormous heating fi X-rays (and gamma rays)

Determine mass of neutron star (black hole) Kepler's 3rd Law Compact object has 'right' mass to be a neutron star ﬁ Evidence for existence of neutron stars

Breakdown of "classical physics" Very strong gravity on surface of Neutron star Escape velocity > 0.5 speed of light ﬁ special considerations

D) Life of stars with different masses Low mass (< 0.4 Ms) H burn White Dwarf Medium mass (≈ 0.4 - 3) H burn Red Giant Mass Loss White Dwarf High mass (≈ 3 - 8) H burn Red Giant Supernova Neutron Star Very high mass (> 8) H burn Red Giant Supernova Black Hole?

83 XI. Relativity 1. Special Relativity a) Principles of Relativity i) "the laws of physics the same to all non-accelerating observers" No matter how fast they are moving relative to each other Dropping a Ball in a Moving Car

Ball falls straight

Ball falls straight From an experiment in a car !!!!!!!!moving withconstant speed you cannot decide whether it is moving

Measuring Speeds in a Moving Car

Truck: 15 m/sec

Railroad: 30 m/sec Speed(Truck) total = Speed(Truck) + Speed(Railroad)

45 m/sec = 15 m/sec + 30 m/sec

No! Truck: 45 m/sec

ii) Speed of light = c the same for everyone

84 Measuring Speeds in a Moving Car

Light: 300,000 km/sec

Flash !

Railroad: 30 m/sec

Speed of Light = Speed of Railroad + Speed of Light 300,000 km/sec = 0.03 km/sec + 300,000 km/sec

Hmpf ???? Light: 300,000 km/sec

To get velocity: we need to measure distance and time b) Einstein's resolution of the dilemma - Time not absolute (passing slower at high speed) i. Traveling twin paradox (traveler stays younger) ii. Simultaneity not absolute - Lengths get contracted at high speed Space time: observers can agree on combinations of space & time c) E = Mc2 or why moving things gain mass Mass can be transformed into energy ﬁ energy source of the stars Then: Energy can also be mass ﬁ M = E/c2

Mass into motion fi Kinetic Energy fi "Kinetic Mass" m -> • as velocity fi c Can't ever get to c!!!! energy goes into increasing mass rather than increasing speed

85 2. General Relativity: A) Basic principles

It feels the same, whether you are pulled by the Earth or pushed by an accelerating rocket or in other words Acceleration is equivalent to gravity

Acceleration Can Cancel Gravity

Constant velocity

I am floating!! Defect No forces!! Elevator I am floating!! No forces!!

Gravity

Earth

based on "Inertial Mass = Gravity Mass" mi = mg B) Effects of Gravity on Time a) Gravitational redshift In accelerated spaceship: detector faster while light is on the way -> Doppler red shift of light In gravity: light looses energy -> Gravity red shift (tests: white dwarfs, precise experiment in lab) b) Gravitational twin paradox Time runs slow near huge mass (test: atomic clocks flown at different elevations) C) Curvature of space Light is bent in gravity fields: Know: light is taking a straight path? Better: light is taking shortest path!! This can be curved! Analogy: on Earth we always take the great circle route as the shortest (transatlantic routes of jet liners) -> Mass (and energy) produce a curved space-time

86 D) Tests of general relativity a) Gravitational deflection of light 1919: First test of Einstein's prediction of gravitational deflection of light During total solar eclipse

Apparent position of star * True *position sun of star Observer

b) Spacetime curvature produces non-Keplerian motion Analogy: ball rolling on a dented tabletop -> The orientation of the orbit of Mercury turns around (like a rosetta) not a perfect ellipse ("perihelion shift") c) Gravitational waves: propagating ripples in space time Observation: Pulsar (a very precise clock!) orbiting neutron star Slowing down due to gravity wave emission (energy loss) When will they be directly observed? E). Black Holes A hole in space time -> everything falls "out of our spacetime" Analogy: A hole in a tabletop -> everything falls through a) Principles

If M > 3(?) Msun, collapse continues Gravity increases and even light can't escape b) Possible example: Cygnus X-1: A special binary X-ray source 30 Msun normal star moves Compact X-ray companion must have > 6 Msun ﬁ evidence that the compact object is a black hole

c) Features of a Black Hole Concentrates mass inside the "Schwarzschild radius" = "event horizon" (Not difficult for super massive black holes > 108 solar masses) Sun would have to be squeezed to a radius of 3 km!! Can only grow: Black Holes dig their own holes in space time Nothing will ever come back! Can only have mass, angular momentum, electric charge No structures "Black holes have no hair"

87 Binary Starsystem With Black Hole

Equal Gravity

Giant Star

Black Hole

Material from Companion Star

X-Rays Gamma-Rays

Impact Velocity ≈ Speed of Light!! Several Billion Kelvin Event Horizon

Black Hole

88 XII. The Milky Way 1. Structure of the Milky Way a) See band of stars in the sky ﬁ we are in disc full of stars

see few stars

see many stars see many stars disc

see few stars

b) Distance determination Use distance of stars to get spatial distribution (spectroscopic parallax (HR diagram)) Kapteyn concluded: We are in the center! ViewView ofof thethe MilkyMilky WayWay inin thethe SkySky andand itsits MeaningMeaning

only few stars

Here are we! only few stars

the same number of stars at the same distances in all directions Jacobus Kapteyn : We are in the center!!

89 only few stars But: What is behind this?

Here are we! only few stars

However, if you are in a fog (surrounded by interstellar dust) you cannot see very far!!! c) Galactic Halo

Shapley used Globular clusters Distance from Cepheids in globulars ﬁ 3D map (1917)

Disc We are not central

us globulars

Galactic Halo consists of: i. Globular clusters (old Population II stars) Left over from pre-galactic-collapse i. Individual Population II stars, high velocities (ejected from globulars?) iii. 21 cm fi hydrogen gas d) Spiral structure The Milky Way has features in common with other spiral galaxies: i. Flat disc (rotation) ii. Emission nebulas (red) and 21 cm fi H gas iii. Radio maps of Milky Way show spiral structure spirals would wind up after a few rotations but: galaxy >20 rotations fi not the same material in arms iv. Young hot (blue) stars light up arms Density waves fi compression fi more self-gravity fi star formation v. Dust

90 2. Mass of the galaxy a) Mass from motion of star clusters Doppler shifts of globular clusters etc. ﬁ "galactic rotation curve"

observed

velocities of stars around the "Keplerian orbits" galactic center

distance from the galactic center

Velocity does not fall off with distance from center i.e. non-Keplerian orbits ﬁ most mass outside disc (not seen in stars) ﬁ missing mass problem.

b) Galactic corona Observed: UV absorption lines ﬁ hot (ions) and turbulent (Doppler) gas Most mass of galaxy? ﬁ missing mass ? What kind? Brown Dwarfs? Black Holes? Strange form of Matter?

3. Galactic center: Exciting observations: i. Expanding & rotating rings (Doppler effect) fi explosions in center? ii. Synchrotron radiation "blob" near center fi explosion? iii. SgrA* - small intense radio source 6 iv. Need 3 x 10 Msun in SgrA* to keep things from flying away SgrA* = super massive black hole (≈100 Msun)? v. Rotating (Doppler) molecular disc around SgrA* vi. Matter falling in fi energy to power all the bizarre features? vii. Gammas from electron-positron annihilation viii. Other galaxies: rapid central rotation fi super massive black holes?

91 XIII. Galaxies and the Structure of the Universe 1. Proof of other galaxies Shapley - Curtis debate: nebulae in Milky Way or separate galaxies? Hubble: Cepheids in galaxies (1924) Period - Luminosity relation ﬁ distance ﬁ "island universes"

2. Galaxy types a) Spirals Like the Milky Way: disc with spiral arms b) Ellipticals No structure no gas or dust fi no young stars (no star formation) no rotation fi no flat discs, but spheroidal shapes Globular clusters are like very small elliptical galaxies But: ellipticals have very energetic centers (super massive black holes?) while globular clusters have no evidence for central black holes c) Irregulars no regular structure fi distorted by tidal forces?

d) Dwarf and faint galaxies The 'missing mass' in the universe? e) Why ellipticals and spirals? Still a riddle i. Not age - old stars in both ii. Not rotation - won't cause lack of gas & dust in ellipticals iii. Galaxies collide ﬁ ellipticals - Stimulates rapid early star formation (Starburst galaxies?) - Consumes gas & dust which are not available for making young stars - Cancels angular momentum - Ejects hot gas ﬁ another way to explain lack of gas But: no star collisions! (distances still too large)

92 3. Masses of galaxies Doppler effect fi velocities a) Spirals Galactic rotation curves fi velocities fi Mass b) Ellipticals Broadening of lines from stars fi velocities fi Mass Large central velocities fi super massive black holes c) Binary galaxies Individual velocities (Kepler's 3rd law) fi m1 + m2 and m1/ m2 d) Galactic clusters Velocities of member galaxies All cases: deduce amount of gravity needed to keep things from flying apart Much more matter than observed in stars is needed to keep the structures together! fi Dark matter problem everywhere

93 4. Galaxy Clusters a) Local group Where our Milky Way and Andromeda is in b) Types of Clusters Regular clusters (spherical shape): contain only ellipticals Irregular clusters: contain ellipticals and spirals Evidence in favor of scenario with collisions Regulars fi interactions (collisions?) fi ellipticals and spherical group Regulars: hot X-ray emitting gas between galaxies (from collisions) Regulars: giant ellipticals at center fi "galactic cannibalism"

5. The Galactic Distance Scale and Huge Structures a) Distances from combination of methods Expanding from close to distant Standard candles - "know" luminosity Brightness -> Distance Standard rulers - "know" size Angular size -> Distance Distance Measurements

Standard "Candles" Standard "Rulers"

Luminosity Size

Spectroscopic Parallax Globular Clusters Color of Star Size of largest ones Cepheids Variation Period Galaxies Size of largest ones Supernovae in galaxy clusters Light Curve

Globular Clusters Most luminous ones

Measure: Measure: Apparent Magnitude Angular Size

Distance

94 b) Hubble's Law (1929) Observed: Large redshift ﬁ object far away vaway = H x Distance (H: Hubble constant) Hubble's Law can be used the other way around: Redshift ﬁ distance (galaxy map of universe) c) Superclusters: "Great Wall", sheets and voids (bubbles) - the largest structures in the universe - a riddle - are the voids really empty or full of dark matter - a riddle

95 6. Active Galaxies a) Radio galaxies Energetic jets emerging from their centers b) Seyfert galaxies Spirals with very energetic "star-like" centers Like center of Milky Way, but more energetic c) BL Lac objects Ellipticals with very energetic centers d) Quasars "quasi-stellar radio sources" i. Look star-like, but give radio (synchrotron), IR, UV, X, gamma (Some can be radio-quiet but they are still called quasars.) ii. Huge redshifts (Hubble) fi large distance iii. Distance: If we see them fi huge luminosity iv. Far away fi light needs long time fi objects in early universe v. Time changes fi energy generated in small regions Can't get big object to change quickly Even if it did, we'd see photons arrive at different times fi Energy of 1000's of galaxies generated in the size of the solar system vi. Quasars = cores of forming galaxies? Seyferts, BL Lacs = cores of formed galaxies? fi Evidence for galaxy evolution? All these objects have bright point-like centers fi Evidence for super massive black holes Energy generation: a riddle fi Super massive black holes?

Importance: clues to how & when galaxies form Is black hole formation part of galaxy formation?

96 XIV Cosmology

So far we could test models at many different objects. Cosmology: test only at our one universe Why is the night sky dark? Olbers' paradox Is the universe infinitely large? ﬁ then the infinite number of stars should overlap in the sky ﬁ very bright sky ???

1. Hubble's Law (1929)

vaway = H x distance fi The universe expands Space itself expands, but Not expansion into something Space expands fi photons expand fi "cosmological redshift" Expansion seen in the same way from everywhere Analogy: raisins in a raisin cake when rising due to yeast

2. Models of the Universe - Big Bang: big explosion at start density decreases with time -> clear evolution of distant galaxies -> beginning with hot -> cooling - Steady State: continuous expansion of space but: creation of new matter -> density remains the same -> would see no evolution in distant galaxies Clues?

97 3. Age and Size of the Universe A) Age a) From Hubble's law: Big Bang: Explosion of everything everywhere "together" @ time = 1/H ago (About 15 billion years.) Not an explosion into space: space exploded

Finite age ﬁ "particle horizon" or "observable universe" "On a clear day you can't see forever" because photons from far away haven't had time to reach us. This is why the sky is dark. ﬁ Resolution of Olbers' Paradox

b) From age of stars Globular clusters oldest star clusters (≥ 10 billion years old) checks B) Size Finite or infinite? Finite: observer on edge would see something different -> infinite universe How can an infinite universe have expanded from a tiny start? Analogy (in 2 dimensions): inflating a balloon -> has curved surface -> curved space in the universe? (from gravity: General Relativity)

98 4. Dynamics of the universe a) The universe starts out with a very rapid expansion Gravity slows down the expansion of the universe Consequence: . Real age = 2/3H due to slowing down of expansion (ª 1010 yrs.) Age Problem: globular clusters seem to be older than the universe! b) Critical density (what id the fate of the universe?) Enough mass density to bring all flying masses back by gravity or in other words Is the "escape velocity" of the galaxies not high enough to escape forever? = critical density: infinite universe flat geometry expands forever > Critical density: finite: enough gravity so that space closes in on itself sphere-like geometry enough gravity ﬁ re-contracts ﬁ "big crunch" < Critical density: infinite not enough gravity saddle-like geometry expands forever We need to solve "missing mass problem" or measure curvature of space. <-> Is the 3D universe curved? Test by measuring: Area of sphere (does radiation fall of as 1/distance2?) Is skinny triangle equation correct? Do parallel lines converge or diverge? Volume of sphere (how does density of galaxies vary with distance from Earth?) Escape Velocity and "Critical Mass"

escapes easily escapes barely returns

11.2 km/sec 11.2 km/sec 11.2 km/sec

Rocket

0.5 x 2 x M M M Earth Earth Earth

Size of the Earth constant!

99 5. Background Radiation

Early universe ﬁ hot; dense ﬁ blackbody radiation

At age of about 3x105 yrs photons decouple from matter (universe 1/1000th present size) (less dense; ions + electrons ﬁ H, He) Universe opaque before about 3x105 yrs (many photon - particle collisions) ﬁ we can't see photons from before 3x105 yrs (Curtains of the universe)

Prediction: universe now filled with photons with T = 2.7K (after cooling due to expansion of universe) Detection: 1965: Penzias and Wilson detect 2.7K Blackbody Radiation (Nobel Prize) LightLight asas aa TimeTime MachineMachine inin thethe UniverseUniverse Distance

Quasars Galaxies Curtain Invisible (opaque)

Time Today Big Bang Light 3 x 10 5 years Background 3000 K Radiation Radiation

i) Supports big bang ii) Provides a "standard of rest" Our galaxy and other galaxies are 'falling' toward a "Great Attractor" The expansion is not uniform. A riddle 2.7K photons an absolute reference iii) Early universe very uniform (but not perfectly uniform) Riddle - how did galaxies form so quickly?

100 6. Early and current universe a) Matter dominated universe Now energy of universe dominated by mass (E = mc2), even though Number of photons is about 109 times the number of particles of visible matter b) Radiation dominated universe Before about 3x105 yrs: energy (and gravity) dominated by photons ("In the beginning there was light.") Production of elements: Helium production by fusion in dense, hot early universe: Predict 25% of mass of universe should be Helium, as observed Independent support of Big Bang

101 7. Problems with the model: a) Matter Problem

In the radiation-dominated era (universe < about 106 years old) there were 109 photons 109 + 1 particles of matter 109 particles of antimatter Why was there one extra particle of matter? b) Horizon problem. 2.7K photons in opposite parts of sky have same temperature But those parts were never in contact (particle horizon) before How did they "know" to have the same temperature? c) Smoothness problem. Probably solved by detection of non-uniformity of the 2.7K radiation d) Flatness problem. Universe had to be very flat at the beginning for it to be the way it is now Problems do not point to wrong physics, but the model does not offer an explanation!

8. The Inflationary Universe

- Contact before inflation solves horizon problem - Solves flatness problem Analogy: we 'see' a flat earth because we see only a small part of it - Quantum fluctuations ﬁ non-smoothness, which agrees with the observed non-smoothness of the 2.7K radiation

102 9. Limits of Knowledge

Why are the world parameters exactly as they are? If different by a tiny bit -> Duration of universe either too short or no stars possible -> No life -> no man to observe the universe IntelligentIntelligent LifeLife inin thethe CosmologicalCosmological AlternativesAlternatives

D(t) r < r c

r = r c Size of the Universe r > r c

15 1000 2000 9 t in 10 years today Age of the Universe

Anthropic Principle: a) Strong anthropic principle -> Universe was designed such that man can appear or b) Weak anthropic principle -> We live in one of many possible universes where we are able to exist

Both offer no explanation, but only a constraint what to look for. These are philosophical and not scientific statements! Revised E. Möbius 1/2003

103 104 References for additional reading and as material for Term Paper Textbooks Abell, Morrison, Wolff, Exploration of the Universe, Saunders Publishing, 1991. Textbook. QB45.A16 1991 Arny, T.T., Explorations, an Introduction to Astronomy, Mosby, 1994. Textbook. not in Library Dixon, R.T., Dynamic Astronomy, Prentice Hall, 1991. Textbook. not in Library Kaufmann, W.J., Discovering the Universe, W.H. Freeman, 1992. Textbook. not in Library Kuhn, K., In Quest of the Universe, West, 1991. Textbook. QB45.K86 1991 Pasachoff, J.M., Journey Through the Universe, Saunders Publishing, 1992. Textbook. not in Library Snow, T.P., The Dynamic Universe, West, 1993. Textbook. QB43.2.S66 1983 c.1 Zeilik, M., Conceptual Astronomy, Wiley and sons, 1993. Textbook. not in Library History of Astronomy Copernicus, N., Minor Works, 1992. Solar System, History, Astronomers. QB41.C76213 1992 Gingerich, , The Great Copernicus Chase and Other Adventures in Astronomical History, 1992 History QB15.G56 1992 Observations, Activities in Astronomy Consolmagno, G., D. Davis, Turn left at Orion: a hundred night sky objects to see ..., 1995 QB63.C69 Hoff, D.B., L.J. Kelsey, J.S. Neff, Activities in Astronomy, Kendall/Hunt Publishing Co., 1992. Observations, Activities. not in Library Moeschl, R., Exploring the Sky, Chicago Press, 1993. Observations, Astronomy, Science projects. not in Library Raymo, C., 365 Starry Nights, Prentice Hall, 1982. Observations, Stars, Constellations. not in Library Smith, B.S., R.H. Mesmeyer, New Eyes on the Universe, National Geographic, 185- 1, 2 - 41, 1994. Cosmology, Telescopes, Galaxies. Solar System, Planets etc., Space Exploration Pioneer: First to Jupiter, Saturn and beyond, 1994. Solar System, Planets, Exploration. TL789.8.U6 P563 1984 Solar System, Time Life, 19xx. Solar System, Planets. 523.2.F848 Cattermole, P., Mars, the Story of the Red Planet, Chapman and Hall, 1992. Solar System, Planets, Mars, Exploration. QB 641. C37 1992 (oversize) 105 Hansson, A., Mars and the Development of Life, 1997 Solar System, Planets, Life QB641.H32 1997 Henbest, N., Planets, Penguin Books, 1992. Solar System, Planets, Exploration. (oversize) QB 605. H46 1992 Kippenhahn, R., Bound to the Sun, 1990. Solar System, Planets, Comets. QB43.2.K5413 1990 Lang, K., C. Whitney, Wanderers in Space: Exploration & Discovery in the Solar System, 1991 Solar System, Planets, Comets, Asteroids, Exploration. QB501.L26 1991 Lewis, , Rain of Iron and Ice, 1996 Meteorites QB721.L42 1996 Meadows, J., Space Garbage: Comets, Meteors and Other Solar System Debris, 1985. Solar System, Asteroids, Comets, Meteors. QB741.M37 1985 Norton,, Rocks from Space, Meteorites and Meteorite Hunters, 1994 Meteorites QB755.N67 1994 Rükl, A., Atlas of the Moon, 1992. Solar System, Moon, Atlas. QB595.R8 1992 Sagan, C., Comet, 1985. Solar System, Comets, Meteors. QB721.S34 1985 Sheehan, W., Worlds in the Sky: Planetary Discovery from Earliest Times through Voyager and Magellan, 1992. Solar System, Planets, Asteroids, Exploration. QB601.S543 1992 Steel, D., Rogue Asteroids and Doomsday Comets, Wiley &Sons, 1995. Asteroids, Comets, Impacts on Earth QB651.S74 Wilford, J.N., Mars Beckons, A.A. Knopf, New-York, 1990. Solar System, Planets, Exploration, Mars, Life. QB6411.W558 1990 Extrasolar Planets Croswell, , Planet Quest: The Epic of Discovery of Alien Solar Systems, 1997. Planets, Extrasolar Planetary Systems QB820.C76 1997 Goldsmith, , Worlds Unnumbered: The Search for Extrasolar Planets, 1997 Planets, Extrasolar Planetary Systems QB820.G65 1997 Aurorae, Magnetospheres Davis, N., The Aurora Watcher's Handbook, University of Alaska Press, 1992. Aurorae. Eather, R.H., Majestic Lights, American Geophysical Union, 1980. Aurorae, History of Science. QC971.E18 c.1 Sun, Solar Activity Kippenhahn, R., Discovering the Secrets of the Sun, 1994 Sun QB521.K6313 1994 Wentzel, D., The Restless Sun, 1989 Sun QB521.W46 1989 Zirker, , Total Eclipses of the Sun, Expanded Edition, 1995 Sun, Eclipses QB541.Z57 1995

106 Stars, Galaxies etc. The Universe of Galaxies, Scientific American, W.H. Freeman, 1984. Galaxies. QB857.U55 1984 Particle Physics in the Cosmos, Scientific American, W.H. Freeman, 1989. Cosmology, Nuclear Astrophysics. QB464.P37 1989 Clark, S., Stars and atoms: from the Big Bang to the Solar System, 1995 QB43.2.C53 Kaler, J.B., Stars, 1992. Stars. QB801.K25 1992 Kippenhahn, R., 100 Billion Suns: The Birth, Life and Death of Stars, 1983. Stars. QB806.K5313 1983 Longair, M.S., High Energy Astrophysics, Vol. 1, 1992. ** Nuclear Astrophysics. QB464.L66 1992 Osterbrock, D.E., Stars and Galaxies, Citizens of the Universe, Scientific American, Special, W.H.Freeman, 1990. Galaxies, Luminous Stars, Supernovae. QB857.S73 1990 Rubin, V., Bright Galaxies and Dark Matter, 1997 Galaxies, Dark Matter QB857.R83 1997 Relativity, Spacetime, Black Holes Chaisson, , Relatively Speaking: Relativity, Black Holes, and the Future of the Universe Relativity, Black Holes QC173.55.C46 1988 Taylor, E.F., J.A. Wheeler, Spacetime Physics, W.H. Freeman, 1992. ** Relativity. Wheeler, J.H., A Journey into Gravity and Spacetime, 1990. ** Cosmology, Relativity. QB334.W49 1990 Davies, P., The Edge of Infinity, Simon and Schuster, 1981. Black Holes, Spacetime. QB991N34 D39 c.1 Halpern, P., Cosmic Wormholes, Penguin Books, 1992. Black Holes, Spacetime. Luminet, J., Black Holes, 1992. Black Holes QB843.B55 L8613

Cosmology Cosmology + 1, Scientific American, W.H. Freeman, 19xx. Cosmology. QB981.C82319xx The Universe, Time Life, 19xx. Cosmology, General. 523.B493 Youth Boslough, J., Masters of Time, Addison-Wesley, 1992. Cosmology, Astronomy/Philosophy. QB981.B7269 1992 Davies, P., God and the New Physics, Simon and Schuster, 1984. Cosmology, Religion. BL265.P4 D38 1984 c.1 Davies, Paul, The Last Three Minutes, Basic Books, Harper&Collins Publ., 1994. Cosmology Ferris, Timothy, The Whole Shebang, Simon & Schuster, 1995. Cosmology

107 Goldsmith, D., Einstein's Greatest Blunder?, Harvard University Press, 1995. Cosmology QB981.G594 Kafatos, M., R. Nadeau, The Conscious Universe, Springer, 1990. ** Cosmology , Philosophy. Kippenhahn, R., Light from the Depths of Time, 1987. Cosmology, Galaxies, Quasars. QB981.K5713 1987 Smith, B.S., R.H. Mesmeyer, New Eyes on the Universe, National Geographic, 185-1, 2 - 41, 1994. Cosmology, Telescopes, Galaxies. Taylor, R.J., The Hidden Universe, Simon & Schuster, 1991. ** Cosmology, Missing Mass, Nuclear Astrophysics. QB791.35.T38 1992 Life in the Universe, Scientific American, Special Issue, Vol. 271, No. 4, Oct 1994 Cosmology, Life, Intelligence Unsolved Problems, Space Flight and for Science Fiction Fans: Krauss, L.M., The Physics of Star Trek, Basic Books, 1995. Physics of Science Fiction. Mullane, M., Do Your Ears Pop in Space? John Wiley&Sons, 1997. Space Flight Bahcall, , Unsolved Problems in Astrophysics, 1997. Unsolved Problems QB461.U58 1997

** More difficult

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