Culmination

In observational astronomy, culmination is the passage of a celestial object (such as the Sun, the Moon, a planet, a star, constellation or a deep-sky object) across the observer's local meridian. These events are also known as meridian transits, used in timekeeping and navigation, and measured precisely using a transit telescope. During each day, every celestial object appears to move along a nearly circular path on the celestial sphere due to the Earth's rotation creating two moments when it crosses the meridian. Except at the geographic poles, any celestial object passing through the meridian has an upper culmination, when it comes very near its highest point (the moment when it is nearest to the zenith), and nearly twelve hours later, is followed by a lower culmination, when it comes very near its lowest point (nearest to the nadir). The time of culmination (when the object culminates) is often used to mean upper culmination. An object's altitude (A) in degrees at its upper culmination is equal to 90 minus the observer's latitude (L) plus the object's declination (δ): A = 90° − L + δ. This equation is the basis for the meridian altitude method for latitude determination.