1. The passage of one object across another of larger apparent diameter, such as Mercury or Venus in front of the Sun, or a satellite or its shadow across the face of a planet (see also shadow transit). Mercury and Venus transit the Sun only when they are close to a node of their orbits at inferior conjunction. With Mercury this occurs in early November (ascending node) or early May (descending node), and with Venus in early December (ascending node) or early June (descending node). Transits of Mercury are more common than those of Venus. Because of the relationship between the orbital periods of Venus and the Earth, transits of Venus usually occur in pairs, eight years apart. There is then a gap of more than a century before the next pair. Forthcoming transits of Mercury are on 2019 November 11, 2032 November 13, and 2039 November 7. The next transits of Venus are on 2117 December 11 and 2125 December 8.

http://eclipse.gsfc.nasa.gov/transit/transit.html NASA transits website.

http://sohowww.nascom.nasa.gov/hotshots/2006_11_06/

2. The passage of a feature across the central meridian of a planet.