The culmination of an astronomical object is its passage across the meridian as seen by an observer on earth.

The rotation of the earth gives astronomical objects the appearance of moving across the sky during the course of the night. Objects rise in the east and set in the west. The meridian is a line drawn perpendicular to the horizon, directly due south from the observer. During a sidereal day, an astronomical object will cross the meridian twice: once at its highest point as seen from the earth, and once at its lowest point (when it will be below the horizon). The meridian passage when the object reaches its lowest altitude is the lower 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.