The first observed transit of Venus, where the planet crosses the Sun's face as a small black dot, takes place and is observed by Jeremiah Horrocks and William Crabtree on December 4, 1639.
A transit of Venus, is a rare event occurring in pairs eight years apart every century or more. It was observed by a small group of astronomers in 1639, 1761, 1769, 1874, 1882, 2004, and 2012. these observations historically determined the Sun's distance and solar system scale. The next transits of Venus will occur in December 2117 and December 2125.