[ ăp′ō-ăpsĭs ]

Plural apoapsides (ăp′ō-ăpsĭ-dēz′)

The point at which an orbiting object is farthest away from the body it is orbiting. This point is sometimes given a name that is specific to the body being orbited. For example, the apoapsis of an object orbiting Earth is its apogee (from gaia, the Greek word for Earth), and the apoapsis of an object orbiting the Sun is its aphelion (from hēlios, the Greek word for Sun). According to Kepler's laws of planetary motion, an object is at its lowest velocity at the apoapsis. Compare periapsis.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.