Cook's was one of many astronomical expeditions attempting to observe the 1769 Venus transit. The objective was to measure the solar parallax which is a fundamental quantity for determining the distance from the Earth to the Sun (1 astronomical unit) and, hence, all distances and dimensions in the solar system.
Basically, the problem was to time the exact instant when Venus' disk enters the solar disk from as many different places on Earth as possible. The technique used was first described by Edmund Halley in 1716. Several observations were made of the 1761 transit and even more in 1769. Cook, who was a pretty good astronomer in his own right, escorted a group to Tahiti. Other groups went to California (Chappe), San Domingo (Pingre), Hudson Bay (Wales), Siberia (Vardoe) and still others observed from their home observatories. The values measured for the solar parallax varied from 8.55 sec to 8.88 sec., which is very close to the true value and a great improvement over previous values. Note that the accuracy of the measurements was greatly enhanced by tremendous progress in the 18th century in determining the size and shape of the Earth itself. Best regards, Jim James E. Morrison Astrolabe web pages at: http://myhouse.com/mc/planet/astrodir/astrolab.htm -----Original Message----- From: John Pickard <[EMAIL PROTECTED]> To: [email protected] <[email protected]> Date: Monday, March 15, 1999 8:33 PM Subject: Off topic: transit of Venus in about 1770 Greetings all, When I was a kid at school more years ago than I care to remember, I was taught that Lieutenant James Cook RN came out to Australia in 1770 (or was it 1772??) to have a look around, and also to observe the "transit of Venus" in Tahiti. OK, I know what the ToV is, but why go half-way round the world at great expense and logistic difficulty just to see it? No one ever explained this to me. Apparently the education department assumed that it was self-evident! So my question (which I am sure will be answered) is simple: why would anyone cross the road (let alone the world in a small sailing ship) just to see a ToV? Thanks, John Dr John Pickard Senior Lecturer, Environmental Planning Graduate School of the Environment Macquarie University, NSW 2109 Australia Phone + 61 2 9850 7981 (work) + 61 2 9482 8647 (home) Fax + 61 2 9850 7972 (work)
