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3. Astronomy the oldest science, and the newestSuppose you watch the sun set over a calm oceanwhile lying on the beach, st...
3.1 The starry sky                 Mercury: sao Thủy, Venus: sao Kim                 Mars: sao Hỏa, Jupiter: sao Mộc      ...
• 100000ly across                                • Solar system:                                790000km/h                ...
Aristotle (340 B.C.) ‘On the Heavens’- The earth’s shadow in an eclipse was round- the North Star appeared lower in the sk...
S      1   =       , ϕ = 87 ,                   oL cos ϕ     S18 < < 20     L               Scorrect value    = 390       ...
Eratosthenes (276 B.C.)circumference of the Earth36690km – 40075kmHipparchus (146 B.C.)-Star chart 850 entries-brightness-...
Location on Earth• latitude lines• longitude lines(meridian lines)
Celestial sphere Constelations
Earth’s seasons• Earth’s equator remains tilted at about 23.5°• the northern and southern hemispheres experienceopposite s...
Equinoxes and solstices    (a) autumnal equinox ; (b) summer solstice ;    (c) vernal equinox ; (d) winter solstice
Tides
3.2 Light and Telescopes     What is light?
Radiation laws:    Wien’s law: λmax=0.3/T                    λ- cm, T – K Stefan-Boltzmann law: F=σT4 F – energy fluxHotte...
Astronomical observations: 2 atmospheric windows- optical/visible light- some infrared and radio windows→ dark sites, dry,...
Optical telescopes: refractive and reflective- size of a telescope = size of its aperture- Eye lens size 5mm- 150 mm teles...
Reflecting telescopes:
Resolving power:depends directly on the size of the aperture andinversely on the wavelength of the incoming lightMagnifyin...
Useful magnification
Telescope design and selection:Stability is essentialRefractors:• rugged and require less maintenance• image quality and r...
planned for2020
Radio telescope:• objects that emit powerful radio waves but littlevisible light• radio sources behind interstellar dust c...
Radio astronomy  (1931)Largest single: 300m dishArecibo Obs., Pueto Rico  Since the 1960s: infrared, ultraviolet, x-ray, g...
Aperture synthesis
3.3. STARSDistances to nearby stars: parallaxSecond of arc = 1/3600o ->1pc=3.26 light yearsSatelite Hipparcos (89) tenfold...
Types of spectra- continuous- emission- absorption
• stellar spectra are absorption spectrums• stars are blazing balls of gas: continuous spectrum• some of the colors are ab...
Fraunhofer ,1814, absorption spectrum of the Sunso far thousands of dark lines, more than 70elements in the chemical compo...
Spectral Classes• U.S. astronomer Annie J. Cannon (1863–1941)examined the spectra of 225,300 stars• Spectral Classes: OBAF...
One can identify a new star’s spectral class andprobable temperature by comparing its spectrum tothe images in Figure 3.8
Origin of spectral class characteristics• At extremely high T, as in O stars, gas atoms areionized. Only the most tightly ...
Motions:Austrian physicist Christian Doppler(1803–1853)Wavelengths are shorter (blueshift) or longer (redshift)when the so...
Other properties:- Gas density: collisional broadening- Axial rotation: rotational broadening- Magnetic field: Zeeman effect
Distinguish a star’s apparent brightness—the way the star appears in the sky—from its luminosityPropagation: B=L/(4πd2)B: ...
Hertzsprung–Russell diagram Ejnar Hertzsprung, Danish (1873-1967) Henry Russell, American (1877-1957) A basic link between...
-Main sequence:90%, hydrogenfusion-Supergiants, giants:1%, thermonuclearreactions-White dwarfs: 9%,dim, no reactions-Red d...
Sizes and densities:- Stefan-Boltzmann law L = 4πR2σT4- Red giants: very low density compared to the Sun- White dwarfs: 1 ...
Mass-Luminosity relation: the more massive a star is, the more luminous it isSun,M  = 2 × 1030 kg,333,000 times themass o...
3.4 STELLAR EVOLUTIONBirth:- interstellar dust and gas, nebulae, emission nebulae(hot, thin gas 100-1000 solar masses)- pr...
Evolution into main-sequence stars
Why stars shine• main sequence star: an adult star• very slow evolution• energy source: nuclear fusion reactionshydrogen →...
Old age• A star will shine until all the hydrogen → helium• Our Sun: an average medium-sized starhas been shining for abou...
Red giants:- core hydrogen fusion ceases- helium core contracts, rising temp.- shell hydrogen fuse faster, luminosity incr...
• Our Sun, like all stars, is expected to change into ahuge red giant when it dies• That red giant Sun will shine so brigh...
Synthesis of heavier elements-100 mil. K: nuclear fusion reactionshelium → carbon and heavier elements- 2 populations ofst...
Variable stars• Most stars change from red giants to pulsatingvariable stars before they finally die• expand and contract ...
2 properties:- very luminous up to 104 L- period-luminosity relation→ distance marker < 10 mil ly• Cepheid variables: per...
The deaths of stars:depends crucially on the massLow mass stars → nebula+coreour Sun will become so big that it will swall...
Exploding stars:High-mass stars → supernova- 8 or more times the Sun’s mass- 600 mil. K, carbon fuse into magnesium- fusio...
Superdense stars:left behind by very massive starsneutron stars, degenerate neutron pressure- more mass than the Sun, 16km...
Black holes:- Core>3M , another possibility: white dwarfs orneutron stars + companion stars in a bin. system- Schwarzschi...
-Rotating black hole:ring-shaped singularity,accretion disk,wormholes-Falling into a blackhole:an infinite voyage, timedil...
3.5 GALAXIESMilky way: 200 bil. Stars, interstar average distance 5 ly
Our Sun: 250 km/s, 220 mil. years 1 revolution- 25 000 ly from the center- Milky way: 100000 ly across, 10000ly nuclear bu...
Theory check of stellarevolution: all stars leave themain sequence as they ageBelow: data,M45 young 70 mil. yearsM3: old, ...
Mapping our Galaxy:• We cannot look > 1000 ly because of dust clouds• spiral structure is mapped by detecting radio waveso...
• The nucleus: very massive, compact object ringedby hot, chaotic gas clouds and dust calledSagittarius A*• A massive blac...
Beyond the Milky Way Galaxy: • Our Galaxy was the only one recognized until 1924 • U.S. astronomer Edwin Hubble (1889–1953...
Classification:
Groupings:- Our galaxy, local group of 40 members- Regular clustersActive galaxies: central massive object, such as ablack...
Mysterious quasars: quasi-stellar radio source- nonstellar spectra, dominated by emission lines- More than 100000 are know...
3.6 THE UNIVERSEThe expanding universe: cosmological redshiftGreatest redshifts: more distant and earlier erasCosmological...
H and K ofionized calcium
Standard Big bang theory:- Olber’s paradox- 13.7 bil. years- all matter and radiation were packed together- at 10-43 secon...
k=-1k=1
Inconstant Hubble constant: - data: deceleration in the past, acceleration now - deceleration if gravity acts alone - dark...
Cosmic background radiation:- big bang shortwave radiation- now microwave- uniform, isotropic, 2.7K- observed in 1965, Arn...
Shape and size
3.7 THE SUN
Distance:• The Sun and its planets formed from a rotatingcloud of interstellar gas and dust ∼ 5 bil. years ago• The Sun ha...
The Sun’s structurea) coronaarified, hot gas  mil. Kb) chromospherelows red, hydrogen gas  ∼ 15000Kc) photosphere 5800Kd) ...
4 1H → 4He + neutrinos + gamma-ray photons
Solar neutrinos• light provides few clues about the core• 1014 neutrinos/m2/s• exceedingly difficult to detect• R. Davis (...
RotationThe period of rotation• at the equator∼ 25 days• slower at middlelatitudes• slowest at the poles∼ 35 days         ...
Sunspots• cool blotches on thephotosphere• 4200K• few hours-few months• 2-10 times the Earth• appear in group• most violen...
Solar cycle• At any one time > 300 sunspotsor none at all - may appear• The number regularly rises and falls ina ∼ 11-year...
Magnetism• Sunspots are like huge magnets• thousands of times > Earth’s magnetic field• measuring Zeeman spectral line-spl...
Flares and coronal mass ejections• A flare: tremendous outburst of radiation and material• occur near sunspots• energized ...
How solar eruptions affect Earth• as much energy as a billion hydrogen bombs• Gamma-, X-, and ultraviolet-rays in 8.3 minu...
3.8 THE SOLAR SYSTEM
Origin: solar nebular modelcounterclockwise as seen from above, inferior, superiorKuiper (1905-73) belt: icy primordial ob...
Day names
Moon phases  • Full Moon: 12.37 times a year  • faint earthshine  • synodic month or lunation: 29.5 days
History:-150 A.D. Alexandrian Ptolemy, geocentric model- Polish Copernicus 1543, heliocentric
The phases of Venus
• Galilei (1564-1642), 4 moons orbiting Jupiter-The Church vindicated Galilei in 1992• German Kepler (1571-1630): Kepler’s...
Moon’s orbital motion:Sidereal month (one trip around Earth) 27.3 days
Terrestial planets: Mercury, Venus, Earth, MarsJovian planets: Jupiter, Saturn, Uranus, Neptune
3.8 The PlanetsMercury:• fastest, craters• axis of rotation is vertical, no seasons,• very hot 430oC – bitter cold - 180oC...
Venus: reflecting atmosphere, 97% CO2, temp.480oC (greenhouse effect), pressure 90 atm., dry, rocky
Planet Earth (1) Crust ∼35 km; (2) mantle ∼ 2880 km; (3) core ∼ 3470 km• crust: lightweight rocks such as granite and basa...
Plate tectonics• 2.5 cm/year• magma convection powers the drift• similar plant and animal fossils
Magnetism:• generated by its rotating liquid iron-nickel core• Reversed at irregular intervals(tens of thousands – hundred...
Mars
- There are seasons, -80oC - -5oC- massive volcanoes- the planet’s crust ∼ 50 km thick, does not drift- no liquid surface ...
Jupiter:- 318 times the mass of Earth- Were it 80 times more massive, nuclear fusionreactions could have started- thick, d...
at least 63
Saturn:• 2nd largest,• 9 rings, consist of billionsof dust- to house-sizewater ice particles• huge multilayered gasball of...
Uranus:- discovered with a telescope (1781)- Double the size of the solar system- Mystery till Voyager 2 (1986)- axis of r...
Neptune:- triumph of theor. astronomy:Uranus did not follow the predicted path.John Adams (1819–1892) in England andUrbain...
Dwarf planets• Pluto, Eris, Ceres: first dwarf planetsin this new category defined in 2006 by theInternational Astronomica...
THE MOONSynchronous rotation:The Moon rotates on its axis every 27.3 days, thesame amount of time it takes to travel aroun...
Size and density• The distance to the Moon: accuracy of a fewcentimeters by timing how long it takes a laserlight beam to ...
CratersHistory:-Oldest rocks, 4.3 bil years old-Youngest, from the maria,3.1 bil years old-impact-ejection hypothesis- coo...
max. 7 eclipses/year
COMETSImportant: original material
Tails point away from the Sun(a)Ion tail(b)Dust tail  Origin: Oort cloud (100 bil comets), Kuiper belt
X. LIFE ON OTHER WORLDS- ability to reproduce and metabolism- Fiery Earth’s earliest atmosphere: amino acids- Hydrothermal...
-Multicelled organisms: a billion years ago  - first fish: 425 mil years ago  - reptiles: 325 mil years ago  - dinosaurs: ...
The odds:(1)The number of stars in our galaxy 200 bil(2)The fraction that have planets(3)The average number of planets sui...
Extrasolar planetary systems:Circumstellar disks: thick-> planets forming,thin -> already formed1. Astrometry: tiny wobble...
Star probes:- Pioneer 10: Juiter 1973, beyound Neptune’s orbit 83- Pioneer 11 followed in 1990- Voyagers 1 and 2 are now a...
Inventions from outer space:-Smoke detectors-Laser-eye surgery-Magnetic-resonance imaging-Exercise machines-Search and res...
Space isn’t remote at all. It’s only an hour’s   drive away if your car could go straight                  upwards.   Sir ...
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
Fy12 astronomy
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Fy12 astronomy

  1. 1. 3. Astronomy the oldest science, and the newestSuppose you watch the sun set over a calm oceanwhile lying on the beach, starting a stopwatch justas the top of the sun disappears. You then stand,elevating your eyes by a height h=1.7m, and stop thewatch when the top of the sun again disappears.If the elapsed time on the watch is 11.1 s, whatis the radius of the Earth?
  2. 2. 3.1 The starry sky Mercury: sao Thủy, Venus: sao Kim Mars: sao Hỏa, Jupiter: sao Mộc Saturn: sao Thổ, Uranus: Thiên vương tinh Neptune: Hải vương tinh
  3. 3. • 100000ly across • Solar system: 790000km/h 220mil years – one tripThe solar system in the Milky Way galaxy
  4. 4. Aristotle (340 B.C.) ‘On the Heavens’- The earth’s shadow in an eclipse was round- the North Star appeared lower in the sky in the south- the sails of a ship come into view before the hullAristarchus (310 B.C.)-Moon-Sun angle at half moon is 87o → the Sun is 20 timesfarther from us than is theMoon-Lunar eclipse: The diameter of the Earth is 3 times larger than that of the Moon
  5. 5. S 1 = , ϕ = 87 , oL cos ϕ S18 < < 20 L Scorrect value = 390 L
  6. 6. Eratosthenes (276 B.C.)circumference of the Earth36690km – 40075kmHipparchus (146 B.C.)-Star chart 850 entries-brightness-magnitudePtolemy (100), 765-> Arabic, a few centuries later, MuslimSpain->Latin -> Church dogmaEinstein, at age 16:‘What would the world look like if I weresitting on a beam of light, moving at the speed of light’
  7. 7. Location on Earth• latitude lines• longitude lines(meridian lines)
  8. 8. Celestial sphere Constelations
  9. 9. Earth’s seasons• Earth’s equator remains tilted at about 23.5°• the northern and southern hemispheres experienceopposite seasons• seasonal variations in the length of days and nights
  10. 10. Equinoxes and solstices (a) autumnal equinox ; (b) summer solstice ; (c) vernal equinox ; (d) winter solstice
  11. 11. Tides
  12. 12. 3.2 Light and Telescopes What is light?
  13. 13. Radiation laws: Wien’s law: λmax=0.3/T λ- cm, T – K Stefan-Boltzmann law: F=σT4 F – energy fluxHottest stars:blue-whiteCoolest stars: red
  14. 14. Astronomical observations: 2 atmospheric windows- optical/visible light- some infrared and radio windows→ dark sites, dry, thin, steady air
  15. 15. Optical telescopes: refractive and reflective- size of a telescope = size of its aperture- Eye lens size 5mm- 150 mm telescope – 30 times eye lens size→ light-gathering power 900 times greater- 10m telescope – faint stars with brightness of a candleviewed from the moonGalileo Galilei – 1609, refracting 50mm-telescopeBeginner’s – 60mm, largest – 1m - 1897A refracting telescope
  16. 16. Reflecting telescopes:
  17. 17. Resolving power:depends directly on the size of the aperture andinversely on the wavelength of the incoming lightMagnifying power: ratio of the apparent size of anobject seen through the telescope to its size whenseen by the eye alone
  18. 18. Useful magnification
  19. 19. Telescope design and selection:Stability is essentialRefractors:• rugged and require less maintenance• image quality and resolutionReflectors:• greater aperture for the price• easier to make at home• faintest, most distant objects• folded optics reduce the physical length• the primary mirror is supported from behind
  20. 20. planned for2020
  21. 21. Radio telescope:• objects that emit powerful radio waves but littlevisible light• radio sources behind interstellar dust clouds• can be used in cloudy weather and during thedaytimeAperture synthesis: combines data from two or moretelescopes to simulate one very large aperture
  22. 22. Radio astronomy (1931)Largest single: 300m dishArecibo Obs., Pueto Rico Since the 1960s: infrared, ultraviolet, x-ray, gamma ray telescopes
  23. 23. Aperture synthesis
  24. 24. 3.3. STARSDistances to nearby stars: parallaxSecond of arc = 1/3600o ->1pc=3.26 light yearsSatelite Hipparcos (89) tenfold, 1600ly - 1% diameter of ourgalaxy. Gaia mission (2013), tens thousands ly
  25. 25. Types of spectra- continuous- emission- absorption
  26. 26. • stellar spectra are absorption spectrums• stars are blazing balls of gas: continuous spectrum• some of the colors are absorbed in the atmosphere,
  27. 27. Fraunhofer ,1814, absorption spectrum of the Sunso far thousands of dark lines, more than 70elements in the chemical composition of the Sun
  28. 28. Spectral Classes• U.S. astronomer Annie J. Cannon (1863–1941)examined the spectra of 225,300 stars• Spectral Classes: OBAFGKMLT• All visible stars are roughly uniform in composition,made mostly of hydrogen and helium• differences in the dark line patterns: different surfacetemperatures
  29. 29. One can identify a new star’s spectral class andprobable temperature by comparing its spectrum tothe images in Figure 3.8
  30. 30. Origin of spectral class characteristics• At extremely high T, as in O stars, gas atoms areionized. Only the most tightly bound atoms such assingly ionized helium survive• Around 5800 K, as in G stars such as our Sun, metalatoms such as iron and nickel remain undisrupted• Below 3500 K, as in M stars, even molecules such astitanium oxide can exist.
  31. 31. Motions:Austrian physicist Christian Doppler(1803–1853)Wavelengths are shorter (blueshift) or longer (redshift)when the sourse moves toward or away from us
  32. 32. Other properties:- Gas density: collisional broadening- Axial rotation: rotational broadening- Magnetic field: Zeeman effect
  33. 33. Distinguish a star’s apparent brightness—the way the star appears in the sky—from its luminosityPropagation: B=L/(4πd2)B: (apparent) brightnessL: luminosityd: distanceThe Sun’s luminosity is equivalent to 3850 billiontrillion 100-watt light bulbs shining all together.
  34. 34. Hertzsprung–Russell diagram Ejnar Hertzsprung, Danish (1873-1967) Henry Russell, American (1877-1957) A basic link between luminosities and temperatures a connection exists between a star’s luminosity and its temperature
  35. 35. -Main sequence:90%, hydrogenfusion-Supergiants, giants:1%, thermonuclearreactions-White dwarfs: 9%,dim, no reactions-Red dwarfs: lowmass stars-Brown dwarfs: substellar,no stable fusion
  36. 36. Sizes and densities:- Stefan-Boltzmann law L = 4πR2σT4- Red giants: very low density compared to the Sun- White dwarfs: 1 spoon – several tons on earthSpectroscopic distance determination:Spectrum→Luminosity class + T + HR diagram →Luminosity + apparent brightness+ L= 4πd2B (propagation)→ distance d (<3000ly)
  37. 37. Mass-Luminosity relation: the more massive a star is, the more luminous it isSun,M  = 2 × 1030 kg,333,000 times themass of Earth.
  38. 38. 3.4 STELLAR EVOLUTIONBirth:- interstellar dust and gas, nebulae, emission nebulae(hot, thin gas 100-1000 solar masses)- protostars form in cold, dark nebulae- gravitational contraction (hydrogen)- temperature and pressure rise greatly- 10 mil. K: nuclear fusion- hydrostatic equilibrium Orion Nebula, in the constellation Orion
  39. 39. Evolution into main-sequence stars
  40. 40. Why stars shine• main sequence star: an adult star• very slow evolution• energy source: nuclear fusion reactionshydrogen → helium (hydrogen bombs)• E=mc2• 0.01% of the Sun’s masschanges to sunshine in abillion years
  41. 41. Old age• A star will shine until all the hydrogen → helium• Our Sun: an average medium-sized starhas been shining for about 5 billion years, shouldshine for another 5 billion years• massive, hot, bright stars die fastest• Rigel in Orion: only a few million yearsred dwarfs are the oldest and most numerous mainsequence stars
  42. 42. Red giants:- core hydrogen fusion ceases- helium core contracts, rising temp.- shell hydrogen fuse faster, luminosity increases- contraction and fusion heat up (100 mil. K)- the star expands to gigantic proportions- surface temperature drops and color turns to red
  43. 43. • Our Sun, like all stars, is expected to change into ahuge red giant when it dies• That red giant Sun will shine so brightly that rockswill melt, oceans will evaporate, and life as we knowit on Earth will end
  44. 44. Synthesis of heavier elements-100 mil. K: nuclear fusion reactionshelium → carbon and heavier elements- 2 populations ofstars: Pop. I young,metal richPop. II old,metal poor (early universeconsisted almostexclusively of hydrogenand helium)
  45. 45. Variable stars• Most stars change from red giants to pulsatingvariable stars before they finally die• expand and contract and grow bright andfade periodically• Explanation:- compression → ionized helium which is opaque- expansion, cooling, recombination,transparent, contraction
  46. 46. 2 properties:- very luminous up to 104 L- period-luminosity relation→ distance marker < 10 mil ly• Cepheid variables: period 1-70 days;example: Polaris, the North Star: every 4 daysdistance marker out to10 mils ly• RR Lyrae variables: less than a day.600,000 ly• Long-period Mira variables, 80-1000 days130 ly away
  47. 47. The deaths of stars:depends crucially on the massLow mass stars → nebula+coreour Sun will become so big that it will swallow upMercury, Venus, Earth, and MarsWhite dwarfs:• temperature and pressure go up very high• mostly of electrons and nuclei• cooling, crystallized, an immense diamond• gravity 350,000 times that on Earth• turns to dull red, then black dwarf
  48. 48. Exploding stars:High-mass stars → supernova- 8 or more times the Sun’s mass- 600 mil. K, carbon fuse into magnesium- fusion of heavier elements: oxygen, silicon- iron ends these cycles- core compressed, rebounds -> Type II supernova- heaviest elements such as gold and lead areproduced in the explosion→ our Sun and Earth
  49. 49. Superdense stars:left behind by very massive starsneutron stars, degenerate neutron pressure- more mass than the Sun, 16km across-1 spoon of matter – 100 mils. tons on earth- discovery (1960) - Pulsars: rotating, highly magneticneutron star (Crab pulsar period 0.0333 sec.)- theory: giant rotating magnet → electric generator→ pair production of elec. + positrons, move alongthe curve field →radiation- Superfluidity- Superconductivity- Mass limit 2-3M 
  50. 50. Black holes:- Core>3M , another possibility: white dwarfs orneutron stars + companion stars in a bin. system- Schwarzschild radius RS=2GM/c2 ,Sun 3km, Earth 1cm- boundary no light can get out -> event horizon- further shrink -> singularity- Cygnus X1, 1966, binary stars (>20 candidates)- Supermassive black holes at the center of galaxies106-109 M -3 properties: mass, charge,angular momentum-observation: accretion,gravitational lensing
  51. 51. -Rotating black hole:ring-shaped singularity,accretion disk,wormholes-Falling into a blackhole:an infinite voyage, timedilation, gravitationalredshift, tidal forces-microscopic black hole: sufficient pressure, LHC-Hawking radiation
  52. 52. 3.5 GALAXIESMilky way: 200 bil. Stars, interstar average distance 5 ly
  53. 53. Our Sun: 250 km/s, 220 mil. years 1 revolution- 25 000 ly from the center- Milky way: 100000 ly across, 10000ly nuclear bulgeLocation of stars: star clusters, same age, same origin
  54. 54. Theory check of stellarevolution: all stars leave themain sequence as they ageBelow: data,M45 young 70 mil. yearsM3: old, 8 bil. years
  55. 55. Mapping our Galaxy:• We cannot look > 1000 ly because of dust clouds• spiral structure is mapped by detecting radio wavesof 21-cm wavelength, emitted by hydrogen atoms• large, hot gas clouds: continuous radio emission• molecular hydrogen in dark, cool molecular clouds:infrared and ultraviolet wavelengths• gravitation of luminous matter cannot explainobserved velocities of stars and gas clouds,gravitational lensing• Our visible Galaxy must contain a lot of dark matterand surrounded by a dark matter halo 300000 ly across
  56. 56. • The nucleus: very massive, compact object ringedby hot, chaotic gas clouds and dust calledSagittarius A*• A massive black hole powers the central gas flowsand luminosityFormation: over 13 billion years ago- 300000 years after Big bang,atoms of hydrogen and helium began to form- Density fluctuations- baryonic matter condense within cold dark matter
  57. 57. Beyond the Milky Way Galaxy: • Our Galaxy was the only one recognized until 1924 • U.S. astronomer Edwin Hubble (1889–1953): proved that some “nebulas” were really galaxies • Large and Magellanic Clouds: companions of our Galaxy • The Andromeda Galaxy: the closest similar to ours
  58. 58. Classification:
  59. 59. Groupings:- Our galaxy, local group of 40 members- Regular clustersActive galaxies: central massive object, such as ablack hole = mil. Suns
  60. 60. Mysterious quasars: quasi-stellar radio source- nonstellar spectra, dominated by emission lines- More than 100000 are known- Extraordinary power, thousand normal galaxies- extremely compact, 1 light-day across, not muchbigger than our solar system- Ultraluminous centers of distant galaxies- No nearby quasars, the nearest one 800 mil. lyaway- Highest redshift, 90 % of c, ultraviolet light → redlight on Earth
  61. 61. 3.6 THE UNIVERSEThe expanding universe: cosmological redshiftGreatest redshifts: more distant and earlier erasCosmological principle: homogeneous and isotropicHubble law (1929): v=Hd, H = 23km/sec/mly
  62. 62. H and K ofionized calcium
  63. 63. Standard Big bang theory:- Olber’s paradox- 13.7 bil. years- all matter and radiation were packed together- at 10-43 second: 1032 K- in a few seconds: protons, neutrons, electrons,positrons, neutrino- within minutes: deuterium, helium- 380000 years: cool enough for neutral atoms- several mils. years: stars and galaxies- today: expanding, 74% hydrogen, 24% helium- future: curvature index k (0,-1,1), cosmologicalconstant
  64. 64. k=-1k=1
  65. 65. Inconstant Hubble constant: - data: deceleration in the past, acceleration now - deceleration if gravity acts alone - dark energy: gravitational repulsionMatter and energy:- Critical density for a flat universe: 5 hydrogen atoms/m3- 5% ordinary matter, 23% dark matter → 72% dark energy- massive neutrinos, MACHOs massive compact haloobjects, WIMPs weakly interacting massive particles mayexist
  66. 66. Cosmic background radiation:- big bang shortwave radiation- now microwave- uniform, isotropic, 2.7K- observed in 1965, Arno Penzias and Robert WilsonBig bang questions:- Matter - antimatter- horizon problem: disconnected regions have same T- flatness problem: ρ0=ρc >50 decimal places- magnetic monopoles→ inflation 10-38 – 10-32 secWilkinson microwave anisotropic probe (2001-): tinyfluctuations
  67. 67. Shape and size
  68. 68. 3.7 THE SUN
  69. 69. Distance:• The Sun and its planets formed from a rotatingcloud of interstellar gas and dust ∼ 5 bil. years ago• The Sun has > 99 percent of the mass
  70. 70. The Sun’s structurea) coronaarified, hot gas mil. Kb) chromospherelows red, hydrogen gas ∼ 15000Kc) photosphere 5800Kd) convection zonee) radiation zone ) core 15 mil K, 200 bil. atm
  71. 71. 4 1H → 4He + neutrinos + gamma-ray photons
  72. 72. Solar neutrinos• light provides few clues about the core• 1014 neutrinos/m2/s• exceedingly difficult to detect• R. Davis (1960s), Brookhaven Nat. Lab.100,000 gallons of perchloroethylene (C2Cl4)huge tank deep underground37 Cl → radioactive 37Ar• Kamiokande, M. Koshiba (1980s), 3000 tons of water,1100 light detectors, recoiling electron emits light,only a fraction of the expected flux was detectedSuper Kamiokande (1998), neutrino oscillation• Sudbury Neutrino Obs. in Canada (2004): 3 types
  73. 73. RotationThe period of rotation• at the equator∼ 25 days• slower at middlelatitudes• slowest at the poles∼ 35 days (1999)
  74. 74. Sunspots• cool blotches on thephotosphere• 4200K• few hours-few months• 2-10 times the Earth• appear in group• most violent activity
  75. 75. Solar cycle• At any one time > 300 sunspotsor none at all - may appear• The number regularly rises and falls ina ∼ 11-year cycle• most active with greatest outbursts of energyand radiation for about 4.8 years• 6.2 years solar activity lessens• The current cycle began in 2008
  76. 76. Magnetism• Sunspots are like huge magnets• thousands of times > Earth’s magnetic field• measuring Zeeman spectral line-splitting• A weaker magnetic field spreads over the whole Sun• The polarity is reversed every 11 years:22-year solar cycle
  77. 77. Flares and coronal mass ejections• A flare: tremendous outburst of radiation and material• occur near sunspots• energized by strong magnetic fields magnetic reconnection 2×106 K
  78. 78. How solar eruptions affect Earth• as much energy as a billion hydrogen bombs• Gamma-, X-, and ultraviolet-rays in 8.3 minutes.• Flare particles arrive a few hours or days later• These could destroy all life if Earth were not shieldedby its magnetic field and atmosphere.• risky for airplane passengers, astronauts, andspacecraft electronics• geomagnetic storms: compasses don’t work• atmospheric storms, satellite damage, surges inelectric power and telephone lines, and blackouts.• drag on spacecraft, satellites may plunge.The U.S. space station Skylab (73-79) was a casualty
  79. 79. 3.8 THE SOLAR SYSTEM
  80. 80. Origin: solar nebular modelcounterclockwise as seen from above, inferior, superiorKuiper (1905-73) belt: icy primordial objects, predicted 1951
  81. 81. Day names
  82. 82. Moon phases • Full Moon: 12.37 times a year • faint earthshine • synodic month or lunation: 29.5 days
  83. 83. History:-150 A.D. Alexandrian Ptolemy, geocentric model- Polish Copernicus 1543, heliocentric
  84. 84. The phases of Venus
  85. 85. • Galilei (1564-1642), 4 moons orbiting Jupiter-The Church vindicated Galilei in 1992• German Kepler (1571-1630): Kepler’s laws- ellipse, the Sun at one focus- const. area- P2 ∼ a3• Isaac Newton (1642-1727)
  86. 86. Moon’s orbital motion:Sidereal month (one trip around Earth) 27.3 days
  87. 87. Terrestial planets: Mercury, Venus, Earth, MarsJovian planets: Jupiter, Saturn, Uranus, Neptune
  88. 88. 3.8 The PlanetsMercury:• fastest, craters• axis of rotation is vertical, no seasons,• very hot 430oC – bitter cold - 180oC,• very thin, unstable atmosphere
  89. 89. Venus: reflecting atmosphere, 97% CO2, temp.480oC (greenhouse effect), pressure 90 atm., dry, rocky
  90. 90. Planet Earth (1) Crust ∼35 km; (2) mantle ∼ 2880 km; (3) core ∼ 3470 km• crust: lightweight rocks such as granite and basalt• mantle: dense silicate rock• core: molten, metallic layer, probably a solid center• Atmosphere: 78% nitrogen, 21% oxygen, half <6km• Sun’s ultraviolete light produces ozone
  91. 91. Plate tectonics• 2.5 cm/year• magma convection powers the drift• similar plant and animal fossils
  92. 92. Magnetism:• generated by its rotating liquid iron-nickel core• Reversed at irregular intervals(tens of thousands – hundreds of thousands years)• deflects charged particles from the solar wind
  93. 93. Mars
  94. 94. - There are seasons, -80oC - -5oC- massive volcanoes- the planet’s crust ∼ 50 km thick, does not drift- no liquid surface water- ancient catastrophic flooding- water in ice and vapor form- The atmosphere is too thin to block the deadlyultraviolet rays from the Sun,95% CO2- Perhaps life formed on Mars inthe distant past. Possiblymicrobes still survive
  95. 95. Jupiter:- 318 times the mass of Earth- Were it 80 times more massive, nuclear fusionreactions could have started- thick, dynamic, observable atmosphere,mostly hydrogen and helium- Earth-size solid core- Great red spot: a colossal storm observed 300 years- Jupiter’s atmosphere may be similar toEarth’s primitive one
  96. 96. at least 63
  97. 97. Saturn:• 2nd largest,• 9 rings, consist of billionsof dust- to house-sizewater ice particles• huge multilayered gasball of mostly hydrogen + < half as much helium• central iron-silicate core surroundedby a metallic hydrogen layer• mass 95 Earth,• volume 844 times• could float in water• 29.5 years to orbit the Sun
  98. 98. Uranus:- discovered with a telescope (1781)- Double the size of the solar system- Mystery till Voyager 2 (1986)- axis of rotation // orbit plane (98o),possibly collision with a planet-size body- Each pole gets 42 years of continuoussun light-atmosphere: 82.5% hydrogen, 15.2% He,2.3% methane (CH4)- No cloud feature (low internal heat)
  99. 99. Neptune:- triumph of theor. astronomy:Uranus did not follow the predicted path.John Adams (1819–1892) in England andUrbain Leverrier (1811–1879) inFrance calculated that its motionwas being disturbed by anotherplanet’s gravity.In 1846 Johann Galle (1822–1910)at the Berlin Observatoryin Germany pointed to the predicted spot andfound Neptune- great dark spot (1989) giant stormof the size of Earth
  100. 100. Dwarf planets• Pluto, Eris, Ceres: first dwarf planetsin this new category defined in 2006 by theInternational Astronomical Union• After astronomers saw bigger Eris and other similarKuiper Belt objects, they reclassified Pluto
  101. 101. THE MOONSynchronous rotation:The Moon rotates on its axis every 27.3 days, thesame amount of time it takes to travel around Earth:The same side of the Moon face Earth at all times Tidal locking
  102. 102. Size and density• The distance to the Moon: accuracy of a fewcentimeters by timing how long it takes a laserlight beam to reach reflectors there and return.• diameter of the Moon: 3476 km, ¼ that of earth• average density is 3.34 t/m3, ∼ 3⁄5 that of Earth• gravity ∼1⁄6 that of Earth
  103. 103. CratersHistory:-Oldest rocks, 4.3 bil years old-Youngest, from the maria,3.1 bil years old-impact-ejection hypothesis- cooled off 3 bil years ago-Airless, dry, stable surface
  104. 104. max. 7 eclipses/year
  105. 105. COMETSImportant: original material
  106. 106. Tails point away from the Sun(a)Ion tail(b)Dust tail Origin: Oort cloud (100 bil comets), Kuiper belt
  107. 107. X. LIFE ON OTHER WORLDS- ability to reproduce and metabolism- Fiery Earth’s earliest atmosphere: amino acids- Hydrothermal vents on the ocean floor- a billion years: RNA and DNA, genetic codes- a common virus is a strand of DNA or RNA- Algae and bacteria fossils in rocks 3 bil. years old
  108. 108. -Multicelled organisms: a billion years ago - first fish: 425 mil years ago - reptiles: 325 mil years ago - dinosaurs: 65 mil years - humans 40000 yearsSun’s habitable zone: between Mars and Venus-Some plants and microbes can survive on Mars
  109. 109. The odds:(1)The number of stars in our galaxy 200 bil(2)The fraction that have planets(3)The average number of planets suitable for life(4)The fraction of life starts that -> intelligent organisms(5)The fraction of int. species that have attempted comm.(6)Guess average lifetime of a civilization-> 1 (ours) to a million civilizations
  110. 110. Extrasolar planetary systems:Circumstellar disks: thick-> planets forming,thin -> already formed1. Astrometry: tiny wobble in the path of the star2. Spectroscopy: periodic Doppler shifts. First reportedin 1995, many more followed3. Photometry: light output, first reported in 19994. Gravitational microlensing
  111. 111. Star probes:- Pioneer 10: Juiter 1973, beyound Neptune’s orbit 83- Pioneer 11 followed in 1990- Voyagers 1 and 2 are now at the edge of our solar system,should return data till 2020-One coded message was radioed (1974) -> M13 in theconstellation Hercules 24000ly away, answer 48000 years-Search for extraterrestrialintelligence (SETI)2 strategies:-All-sky survey- targeted search, 100ly ofEarth 1-3000MHz
  112. 112. Inventions from outer space:-Smoke detectors-Laser-eye surgery-Magnetic-resonance imaging-Exercise machines-Search and rescue technology-Satellite imagery-Computer enhanced imaging-Plants that purify sewage-Electrolytic water filter-Silicon ribbing for racing swimsuits, Speedos-Supercomputers-Ergonomic chairs for the elderly-Clean labs.
  113. 113. Space isn’t remote at all. It’s only an hour’s drive away if your car could go straight upwards. Sir Fred Hoyle, in the London Observer, 1979Reference: Dinah L. Moché ‘Astronomy, a self-teaching guide’ 7th edition, John Wiley & Sons, 2009 End of Chapter

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