American Scientist

Lunar month
The Moon completes one orbit around the Earth (a sidereal month), in 27.3 days. Because the Earth is also orbiting the Sun, it takes two more days for the Moon to complete its cycle of phases (a synodic month).

Elliptical orbit
The Moon’s orbit has an elliptical (oval) shape, although it looks almost like a circle.

Apsidal precession
The Moon’s elliptical orbit orientation changes its orientation, or precesses, with a period of 8.85 years.

Drifting away
Every year the Moon’s orbit is expanding, taking it farther away from Earth by an average of 3.8 centimeters.

Nodal precession
The plane of the lunar orbit is tilted 5 degrees relative to Earth’s orbit around the Sun. It precesses in an 18.6-year cycle.