Yours, Etc.: Origins and Uses of 8 Sign-Offs
"point farthest from the sun" (of a celestial body's orbit), 1670s, a Grecianized form of Modern Latin aphelium, altered by Johannes Kepler based on Greek apo heliou "away from the sun," from apo "away from" (see apo-) + heliou, genitive of helios "sun" (see sol). The whole was formed on the model of Ptolemaic apogaeum (see apogee) to reflect the new helio-centric model of the universe.
The point at which an orbiting body, such as a planet or comet, is farthest away from the Sun. Compare apogee, perihelion.