In astronomy, the culmination of a planet, star or constellation is its transit over an observer's meridian. During a sidereal day, an astronomical object crosses the meridian twice: once at its upper culmination, when it is (approximately) at its highest point as seen from the earth, and once at its lower culmination, its (approximately) lowest point. Often, culmination is used to mean upper culmination. The altitude of an object in degrees at its upper culmination is equal to (90 − L + D), where L is the observer's latitude and D is the object's declination.