Astronomical Transit

The term transit or astronomical transit has three meanings in astronomy:

• A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, hiding a small part of it, as seen by an observer at some particular vantage point. If the first celestial body hides a major part, or all of, the second celestial body, then it is an occultation rather than a transit.
• A transit occurs when a celestial body crosses the meridian due to the Earth's rotation, about halfway between rising and setting. For instance, the Sun transits the meridian at solar noon. Observation of meridian transits was once very important for timekeeping purposes (see transit instrument).
• The term star transit is used for the passage of a star through the eyepiece of a telescope. Precise observations of elevation or time are carried out to determine star positions or the local vertical (geographic latitude/longitude).

The rest of this article refers to the first kind of transit.