Orbit of the Moon the Moon's orbit around Earth, its relative timing varies greatly. In some places on Earth, there is only one high tide per day, whereas others such as Southampton have four, though this is somewhat rare. The notional tidal bulges are carried ahead of the Earth–Moon orientation by the continents as a result of Earth's rotation. The eccentric mass of each bulge exerts a small amount of gravitational attraction on the Moon, with the bulge on the side of Earth closest to the Moon pulling in a direction slightly forward along the Moon's orbit (because Earth's rotation has carried the bulge
Frozen orbit propellant. For most spacecraft, changes to orbits are caused by the oblateness of the Earth, gravitational attraction from the sun and moon, solar radiation pressure, and air drag. These are called "perturbing forces". They must be counteracted by maneuvers to keep the spacecraft in the desired orbit. For a geostationary spacecraft, correction maneuvers on the order of 40–50 m/s per year are required to counteract the gravitational forces from the sun and moon which move the orbital plane away from the equatorial plane of the Earth. For sun-synchronous spacecraft, intentional shifting of the orbit plane (called "precession") can be used