Apoapsis

Given two objects of which one orbits the other, for example a planet and a satellite, apoapsis is the point in the satellite's orbit which is furthest (at the greatest distance) from the planet.

• If the object orbits the Earth, it's also known as apogee.
• If the object orbits the Sun, it's also known as aphelion.
• If the object orbits the Moon, it's also known as apolune.

The point of the closest approach is the periapsis. According to Kepler's laws of planetary motion; as a planet travels in an elliptical orbit, around a star; as the planet approaches the apoapsis, it will decrease in velocity.