The Transit of Venus is a celestial event that occurs when Venus's orbit causes the planet to speed past the slower moving Earth and visibly cross the Sun, partially obscuring it. The Transits of Venus occur in pairs that are eight years apart, and they are separated in time by just over a century. A Transit happens after 121 years, and then a second Transit occurs after eight years. Another pair of Transits does not occur again for 105 years. This pattern (121, 8, 105, 8) is constant.
The most recent Transit of Venus occurred on June 5 and 6, 2012. This is the last Transit of the century. Earlier Transits recorded:
December 4, 1639
June 5, 1761
June 3, 1769
December 8, 1874
December 6, 1882
The next Transit of Venus will not occur until 2117. Transits last between three to seven hours, depending on the route of the Transit.
When observing the Transit, eyes should be protected by using glasses with #14 shade welding glass, a pinhole projector, and a sun funnel. If using a telescope, one should use an appropriate solar filter.
NOTE: William Smith is the primary author of "Apparent Time of the Contacts of the Limbs of the Sun and Venus; With Other Circumstances of Most Note, in the Different European Observations of the Transit, June 3d,1769." David Rittenhouse contributed text and did the calculations. John Lukens also wrote part of the paper. John Ewing is the principal author of "An Account of the Transit of Venus over the Sun, June 3d, 1769, and of the Transit of Mercury Nov. 9th, Both as Observed in the State-House Square, Philadelphia." Joseph Shippen and Hugh Williamson contributed to the paper. Charles Tbomson and Thomas Prior each contributed a paragraph.