June 6, 1760 The transit of Venus over the Sun.
Transits of Venus are rare, coming in pairs, 8 years apart, separated by approximately 120 years. The next such transit, on June 3, 1769, was observed at Tahiti by a party led by legendary mariner Captain James Cook (October 27, 1728 - February 14, 1779), on a voyage on which Cook claimed the continent of Australia in the name of King George III of Britain.
Almaniac Mary Anne Sabo informs me that the next one will be June 8, 2004. Click the link, it's a very cool page.
James Cook and the transit of Venus
History of Venus transits
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