For an object moving in an elliptical orbit about another celestial body, the point of closest approach is called the periapsis (from the Greek peri = near). At this point in the orbit, the object is travelling at its greatest speed (Kepler’s Second Law).

The periapsis is equivalent to the:

• Perihelion: for a celestial body orbiting the Sun.
• Perigee: for a celestial body (in particular the Moon or artificial satellites) orbiting the Earth.
• Periastron: for a celestial body orbiting a star (e.g. in a binary star system).

The point of maximum distance in the orbit is called the apoapsis.

A planet at perihelion in its elliptical orbit around the Sun.

The Moon at perigee in its elliptical orbit around the Earth.