quasiconjunction

Quasiconjunction is a term used in astronomy and by skywatchers to describe an event in which two celestial bodies appear close together in the sky as seen from Earth, but do not meet the formal criterion for a conjunction. A true conjunction usually requires that the two objects share nearly the same geocentric ecliptic longitude (or right ascension). In contrast, a quasiconjunction denotes a small angular separation between the objects, with the exact threshold left to the observer or to the software reporting the event. Thresholds vary and are not standardized; common practice uses angular separations on the order of 1 degree or more, depending on the context and precision of measurements.

During a quasiconjunction, the paired objects can be Mercury and Venus, or a planet with the Moon or Sun, appearing near each other in the sky. The event is mainly observational and can affect planning for viewing, photography, or astrometric measurements because the apparent proximity can complicate separation of the objects. Occultations or mutual transits are possible only when the separation is extremely small and the alignment coincides with the observer’s vantage point, which is relatively rare.

Usage and standardization: the term quasiconjunction is not universally standardized in professional astronomical literature and is more common in amateur astronomy or ephemeris reporting as a descriptive phrase for “near conjunction” or “close approach.” Etymology derives from quasi- meaning “almost” and conjunction, referring to the idea of near alignment.