- The passage of a smaller astronomical object across the face of a
larger one, as in a transit of Venus
or Mercury across the Sun, or the transit
of a moon across its primary. In the latter case, if the transit involves
the moons shadow rather than the moon itself, it is known as a
shadow transit. Transits of Venus
and Mercury can only take place when the planets are close to the nodes
of their orbits at inferior conjunction:
in early December or early June for Venus, and in early November or
early May for Mercury. Only five transits of Venus have been observed,
those of 1639, 1761, 1769, 1874, and 1882; the next is due in 2004.
- The passage of a meridian or surface
marking across the central meridian
of the disk of a rotating planet.
- The instant at which a star or other celestial object crosses the
observers meridian; also known as culimination
or meridian passage.