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Prof Martin Hendry School of Physics and Astronomy, University of Glasgow

Captain Cook and the Cosmic Yardstick. Prof Martin Hendry School of Physics and Astronomy, University of Glasgow. James Cook (1728 – 1779). Ptolemy: 90 – 168 AD. Nicolaus Copernicus (1473 – 1543). Johannes Kepler (1571-1630). Galileo Galilei : (1564 – 1642).

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Prof Martin Hendry School of Physics and Astronomy, University of Glasgow

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

  2. James Cook (1728 – 1779)

  3. Ptolemy: 90 – 168 AD

  4. Nicolaus Copernicus (1473 – 1543)

  5. Johannes Kepler (1571-1630)

  6. Galileo Galilei: (1564 – 1642)

  7. Galileo Galilei: (1564 – 1642)

  8. Galileo Galilei: (1564 – 1642)

  9. Earth-centred model Sun-centred model Sun Sun

  10. How big is this angle?

  11. Sun Earth Venus

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

  13. Getting the Measure of the Solar System Planet Distance Mercury 0.39 Venus 0.72 Earth 1.00 Mars 1.52 Jupiter 5.20 Saturn 9.54

  14. Getting the Measure of the Solar System Planet Distance Mercury 0.39 Venus 0.72 Earth 1.00 Mars 1.52 Jupiter 5.20 Saturn 9.54 How far is an astronomical unit?…

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

  16. ...

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

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

  19. Parallax Shift

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

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

  22. May 7th 2003: Transit of Mercury

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

  24. November 24th 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)

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

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

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

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

  29. The 3rd 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) Captain James Cook “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!”

  30. Mapping the Solar System Captain James Cook 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

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