Anomalistic month, illustration. The extreme points of the Moon's orbit (the apogee and perigee) slowly vary their position (red arrows) over a 3233-day cycle (8.85 years). This adds to the length of the month, leading to what is called the anomalistic month. This has an average length of just over 27 days and 13 hours. Here, the perigee (closest point) is at left, and the apogee (furthest point) is at right. This type of precession is known as apsidal precession.