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

2. How far is Jupiter ??

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

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 Time to full eclipse ~ moon radius Total eclipse time ~ earth radius Moon radius ~ ¼ earth radius Aristarchus of Samos, 310BC- 230BC

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

8. Geocentric (=earth at the center) vs. Heliocentric (=sun at the center) universe Aristotle (384BC - 322BC) ‏ Aristarchus of Samos (310BC - 230BC) ‏ 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 Mars motion according to Heliocentric theory Ptolemy model - consistent with observations !!!

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

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

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. William Herschel (1738 - 1822) Herschel’s 20 foot reflector III. Measuring distance to the stars -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. Friedrich Bessel (1784 - 1845) 1838: First measurement of distance to a star 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. Charles Messier (1730 - 1817): deep sky catalogue of Nebulae “The great debate”: Are nebulae part of the milky way galaxy - or not ? M31 The great debate

23. John Goodricke (1764 - 1786): Discovery of variable stars & Cepheids Mechanism: Envelope contains opaque He 2+ - 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 Size of the milky way: 100.000 l.y. ; Thickness = 1.000 l.y Cepheids in Globular clusters

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

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

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

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

31. Edwin Hubble (1889 - 1953): II. 1929 - Discovery of distance - velocity relation in galaxies Hubble’s law Velocity = Distance  H 0 H 0 = Hubble’s constant = 70 (km/s) / Mpc Mpc = Mega (Million)-parsec; Parsec = paralax-arcsecond =~ 3.3 l.y. Baade (1952) & Sandage (1954) corrected the value of H 0

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

33. Further proofs for universe expansion & “Big bang” Ralph Alpher (1921 - 2007): 1948: Alpher, Bethe, Gamow - H, He production in big bang Alpher, Gamow & Herman - cosmic microwave background (CMB) Universe: 90% H, 9% He 1964: Penzias & Wilson discover 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 by Adam Riess (STScI), Saul Perlmutter (Berkeley) - The universe accelerates !!!

36. The universe, 2008 Wmap