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The measure of Cosmological distances

Asaf Pe’er Space Telescope Science Institute. The measure of Cosmological distances. August 2008. How far is Jupiter ??. I. Science at ancient times. Greece, c. 300BC What is the size of earth ?. Syene, Egipt. First measurement of earth’s radius: Eratosthenes of Cyrene (276BC- 196 BC)‏.

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The measure of Cosmological distances

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  1. Asaf Pe’er Space Telescope Science Institute The measure of Cosmological distances August 2008

  2. How far is Jupiter ??

  3. I. Science at ancient times Greece, c. 300BCWhat is the size of earth ?

  4. Syene, Egipt First measurement of earth’s radius:Eratosthenes of Cyrene(276BC- 196 BC)‏

  5. Eratosthenes: Earth circumference =40000 km Earth radius = 6000 km

  6. Measuring the size of the moon using lunar eclipse Aristarchus of Samos, 310BC- 230BC Time to full eclipse~ moon radius Total eclipse time ~ earth radius Moon radius ~ ¼ earth radius

  7. Given moon radius, distance is simple geometry Distance to the moon ~380.000 km (240.000 mi)‏

  8. Geocentric (=earth at the center) vs.Heliocentric (=sun at the center)universe Aristarchus of Samos (310BC - 230BC)‏ Aristotle (384BC - 322BC)‏ Why Geocentric ?1. "we see" 2. if the earth moves, where is the wind ? 3. Gravity – everything is attracted to the center of the universe 4. Parallax: stars don't move !

  9. Parallax Parsec = paralax-arcsecond =~ 3.3 l.y.

  10. But some stars do move.. Retrograde motion of Mars

  11. The universe according to Ptolemy Ptolemy: 83-161 AD Circle - “Perfect” shape

  12. Mars motion according to Ptolemy Ptolemy model - consistent with observations !!! Mars motion according to Heliocentric theory

  13. II. Rise of Heliocentric Cosmology Nicolaus Copernicus (1473 - 1543) Advantages:1. Correct 2. Simple Disadvantage: 1. Less accurate than geocentric model2. Copernicus was unknown

  14. Tycho Brahe (1546 - 1601): Accurate measurements of planet orbits Johannes Kepler (1571 - 1630): Planets move in ellipses (not circles) around the sun Kepler’s laws of planetary motion helped Neuton to develop the theory of Gravity

  15. Next breakthrough: the Telescope (1608)

  16. Galileo Galilei (1564 - 1642): First astronomer to use a telescope Moon has craters ! (= not perfect sphere !) Jupiter has moons ! (= not everything rotates around earth !)

  17. Even the sun has spots ! (= sun is not perfect !) “Smoking gun”: Venus phases Cannot be explained by Geocentric model

  18. Measuring the distance to the sun Giovanni Cassini (1625 - 1712) 1672- Cassini & Richer measure the distance to Mars Using Kepler’s laws, Cassini deduce the distance to the sun:150.000.000 km = 1 Astronomical unit (1 A.U.)

  19. III. Measuring distance to the stars William Herschel (1738 - 1822) Herschel’s 20 foot reflector • Found new planet (Uranus) • Discover Infra-Red light • First map of the sky: Idea:All the stars are the same.Therefore, bright stars are closer.

  20. Herschel’s model of the milky way: • Stars are ordered in space. We are part of the Galaxy.- But he could not scale the size of the galaxy

  21. 1838: First measurement of distance to a star Friedrich Bessel (1784 - 1845) 61 signi Distance = 100,000,000,000,000 km (= 11 light years) Scaling the milky way: width = 10.000 l.y., (today: 100.000 l.y.) Thickness = 1.000 l.y.

  22. The great debate Charles Messier (1730 - 1817):deep sky catalogueof Nebulae M31 “The great debate”:Are nebulae part of the milky way galaxy - or not ?

  23. John Goodricke (1764 - 1786):Discovery of variable stars & Cepheids Mechanism:Envelope contains opaque He2+ - heated - pressure increases- expansion - radiation escape - cooling

  24. Henrietta Leavitt (1868 - 1921):1908: Discovery of periodicity- Luminosity relation in Cepheids 25 Cepheids at the small Magellanic cloud All at same distance from us

  25. 1917: Shapley & Hertzsprung measured the distance to a Cepheid - allow the use of Cepheids as “Standard candles” 1918: Harlow Shapely measures the milky way Cepheids in Globular clusters Size of the milky way: 100.000 l.y. ; Thickness = 1.000 l.y

  26. What about the nebulae ? Edwin Hubble (1889 - 1953):I. 1923 - Discovery of Cepheids in Andromeda galaxy Distance to M31: 900.000 light years >> Milky way !!

  27. IV. Measuring distance to the galaxies Spectroscopy:measuring the chemical elements in starsFraunhofer, Bunsen, Kirchhoff (1859)

  28. Spectrum of the sun 1868 - Lockyer & Janssendiscover a new element in the sun (He)1860’s - Huggins:stars contain the same elements as the earth.

  29. 1868 - William Hugginsfinds red shift of Sirius,determine its velocity: 45 km/s Red Shift

  30. 1912: Vesto Sliphermeasures red shift of galaxies V ~ 300-1000 km/s Strangley,most of the galaxies are receding from us !

  31. Hubble’s lawVelocity = Distance  H0H0 = Hubble’s constant = 70 (km/s) / Mpc Edwin Hubble (1889 - 1953):II. 1929 - Discovery of distance - velocity relation in galaxies Baade (1952) & Sandage (1954)corrected the value of H0 Mpc = Mega (Million)-parsec; Parsec = paralax-arcsecond =~ 3.3 l.y.

  32. V. The big bang theory and beyond Back in time, all the matter was concentrated in a very small region Albert Einstein (1879 - 1955) 1915: General Theory of relativity -- universe collapse (Gravity); Cosmological constant 1922: Alexander Friedman Universe expands ! 1927: Georges Lemaitre

  33. Further proofs for universe expansion & “Big bang” Ralph Alpher (1921 - 2007): Universe: 90% H, 9% He 1948: Alpher, Bethe, Gamow - H, He production in big bangAlpher, Gamow & Herman - cosmic microwave background (CMB) 1964: Penzias & Wilsondiscover the CMB

  34. 1991- Fluctuations in the CMB (COBE satellite): “embryos” of galaxies Mather & Smoot, 2006 Nobel prize

  35. The future 1998: A surprising twist Astronomers led byAdam Riess (STScI), Saul Perlmutter (Berkeley) - The universe accelerates !!!

  36. The universe, 2008 Wmap

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