A Short History of Astronomy

1. very A Short History of Astronomy Or, what was in Cooks’ secret ‘sealed package’ and why is Venus relevant to Australia?

2. Australian Aboriginal Astronomy • "Ngaut Ngaut" on the banks of the Murray River. These engravings show a series of dots and lines carved in the rock, which, according to the traditional owners, show the "cycles of the Moon”. • http://www.atnf.csiro.au/research/AboriginalAstronomy/Examples/NgautNgaut.htm

3. Astronomy started with the naming of the celestial objects, and later the recording of their movements in almanacs. • 2300BC The Chinese astronomers started star naming • 750BC Babylonians astronomers recognize the 18.6 year cycles in the rising and setting of the Moon. • 585BC Thales predicts a solar eclipse. • Thales was a brilliant mathematician/scientist/philosopher of the day, who rejected supernatural explanations in preference to natural explanations. • The ability to mathematically predict a Cosmic event of such magnitude, propelled astronomers into the industry of astrology, where they were employed by the rich to cast horoscopes. (and the desire to keep the job or ones head , probably led to the development of the The Barnum Statement, still used by astrologers today) • Even the great mathematician and scientist Johannes Kepler compiled prognostications for the Emperor, as a justified means of supplementing his meager income. • But more on Kepler later.

4. Geocentric or Heliocentric? • This debate was perpetuated for well over a millennium, due to the need to overturn religious doctrines. • 388BC Plato - Geocentric in perfect circles. • 270BC Aristarcus of Samos - Heliocentric • 1250CE Najm al-Din al-Qazwini al Katibi - Heliocentric • 1543CE Nicholaus Copernicus - Heliocentric and retains Plato’s idea of perfect circles. • 1610 Galileo Galilei builds a telescope, and confirms by observation, that the Earth moves around the Sun. • It took the Catholic Church a further 350 years to concede that Galileo was right!

5. Galileo and his telescope

6. 1609CE Back to Kepler and his Three Laws of Planetary Motion. • Planets move in elliptical orbits around the sun. • Planets sweep out equal areas in equal times. • The square of the time a planet takes to go around the sun, is proportional to the cube of its distance from the Sun. • This last law is imortant, but the problem lay with the lack of a method to calculate the distance from the Earth to the Sun.

7. The Transit of Venus • Kepler calculated a transit of Venus would occur in 1631, which was not observed. • An exceptional mathematician, Jerimiah Horrocks calculated that a second transit of Venus would occur in 1639. • Horrock’s was the first person (one of only two) to accurately observe and record the second transit. • An act which set into motion the biggest scientific mission the world had ever seen.

8. Horrock’s entered Cambridge at age 13 and made his observation of the Transit of Venus at age 20.

9. Edmond Halley has an idea! • In this famous paper, Halley explained his idea that the duration of the transit of Venus be observed from different parts of the earth, and then the distance to the sun, (1AU) could be determined with simple geometry.

10. A plan is drawn up. • 50 years before the event, Halley calculated the next transit of Venus, due in 1761, and proposed suitable places for observation. • In the preceding years, over 100 teams of astronomers made preparations to observe the transit of Venus from far flung places. • This next piece of astronomical history was not going pass un-noticed.

11. The First Global Astronomical Collaboration. • According to Richard Proctor, the 19th Century Astronomical writer, 176 Astronomers in 117 locations around the world participated. • Why all the excitement? • Because once the distance from the Earth to the Sun (AU) was accurately benchmarked, Kepler’s Third Law could be used to calculate the distance from the sun to all the other planets. • 1AU = 149597870 km (mean)

12. A second attempt! • Transits of Venus occur in pairs, eight years apart, separated by gaps of around 100 years. • Sadly errors in timing the transit meant Astronomers were not happy with the results of the 1761 observations and so made preparations for the transit of 1769. • In 1768 King George III granted the Royal Society £4,000 for the South Sea Voyage and the Admiralty agreed to provide a ship.

13. Enter Captain James Cook • His ability as capable mariner, navigator and scientist, via observations of a solar eclipse in 1766, brought Cook to the attention of the Royal Society. He was subsequently appointed the task of observing the Transit of Venus from Tahiti. A location recommended by Halley. • Cook was also directed by the Admiralty to carry out secret instructions held in ‘a sealed package’, on completion of the scientific observations.

14. The ‘Secret’ Agenda. • On 30 July 1768, the Lords of the Admiralty signed Cooks instructions for the Endeavor voyage, and they were classified as secret. The Admiralty’s sealed instructions held the reasons for supporting his voyage: in addition to observing the transit of Venus, Cook was commanded to find ‘the Great South Land’, a land of great extent that was thought to exist in southern latitudes: :”You are to proceed to the Southward in order to make discovery of the Continent above-mentioned until you arrive in the latitude of 40deg, unless you sooner fall in with it.”

15. Science and Politics • The Royal Society and the Admiralty agreed on a joint venture in which Britain's territorial ambitions could be concealed behind the more benign exploratory goal of expanding knowledge of the solar system. • The ploy worked and Cooks expedition slipped under the radar of the French and Portuguese, who were already active in the Pacific. • Modern Australia owes its existence to a celestial event!

16. William Parkinson Wilson • Wilson was one of four founding professors at Melbourne University. • He established an observatory in Mornington as part of the transit of Venus observations on 9 December 1874. • He had written a report of his findings to his friend Robert Ellery, when on 11 December he died of apoplexy, aged 48. • He is buried in the Moorooduc cemetery.