1. Prof Martin Hendry School of Physics and Astronomy, University of Glasgow Captain Cook and the Cosmic Yardstick

4. James Cook (1728 – 1779)

12. Ptolemy: 90 – 168 AD

15. Nicolaus Copernicus (1473 – 1543)

16. Johannes Kepler (1571-1630)

17. Galileo Galilei: (1564 – 1642)

18. Galileo Galilei: (1564 – 1642)

19. Galileo Galilei: (1564 – 1642)

20. Sun Earth-centred modelSun-centred model

22. How big is this angle?

23. Earth Sun Venus

24. Earth Sun Venus We can use Pythagoras’ theorem!

25. Getting the Measure of the Solar System PlanetDistance Mercury0.39 Venus0.72 Earth1.00 Mars1.52 Jupiter5.20 Saturn9.54

26. Getting the Measure of the Solar System PlanetDistance Mercury0.39 Venus0.72 Earth1.00 Mars1.52 Jupiter5.20 Saturn9.54 How far is an astronomical unit?…

27. http://www.scottishsolarsystem.org.uk

30. ...

31. Eratosthenes: (c 276 – 195 BC) Syene – Alexandria = 5000 stadia Circumference of the Earth = 250000 stadia

32. Aristarchus (310 – 230 BC): Earth – Moon distance from lunar eclipse

34. Parallax Shift

35. Even the nearest star shows a parallax shift of only 1/2000 th the width of the full Moon Parallax Shift

36. Johannes Kepler predicted a transit of Mercury on 29 th May 1607 Instead, he ‘discovered’ sunspots

37. May 7 th 2003: Transit of Mercury

38. Pierre Gassendi (1592 – 1655) Observed a transit of Mercury on 7 th November 1631

39. November 24 th 1639 Jeremiah Horrocks (c1619 – 1641) “The Founder of English Astronomy” (Eyre Crowe, Walker Art Gallery) William Crabtree (1610 - 1644) “Crabtree watching the transit of Venus” (Ford Madox Brown, Manchester Town Hall)

41. Edmond Halley (1656 - 1742) Halley travelled to St Helena in 1677, to map the Southern Skies He observed a transit of Mercury on November 7 th Transit observations could measure the astronomical unit!

42. Methods relied on an accurate estimate for the radius of the Earth In 1669 Jean Picard (1620 – 1682) measured (0.2% error)

43. The 6 th June 1761 Venus Transit o Results were disappointing: o Astronomical Unit lay between 77 million and 97 million miles (20% uncertainty)  Bad weather  Poor global coverage  ‘Black Drop Effect’  Systematic errors o Observations meticulously planned, for many years o ‘Public outreach’ description by James Ferguson o Franco-British cooperation, despite being at war! o 120 astronomers observed from about 60 locations

44. Captain James Cook The 3 rd June 1769 Venus Transit Endeavour arrived in Tahiti on 13 th April 1769 – constructed a fort, and an observatory, at Point Venus Transit observed by Cook, Green and Solander

45. Captain James Cook The 3 rd June 1769 Venus Transit After years of analysis, the results of the 1769 observations were published. e.g. Thomas Hornsby (1771): Cassini de Thury 1 A.U. = 93,726,900 miles (between 90 and 94 million miles) “Happy is our Century, to which has been reserved the glory of being witness to an event which will render it memorable in the annals of the Sciences!”

46. Captain James Cook Mapping the Solar System Irwin Shapiro Bounced RADAR echoes from Venus in 1968 ‘Shapiro Effect’ time delay also a test of General Relativity In 1976 IAU adopted:- 1 A.U. = 92,958,329 miles = 149,597,870 km

52. The next transit: June 5 th /6 th 2012 www.transitofvenus.org

53. Waikoloa, Hawaii

54. www.transitofvenus.org

55. http://www.scottishsolarsystem.org.uk