"point farthest from the sun" (of a celestial body's orbit), 1670s, from Mod.L. aphelium, the modern form an alteration by Johannes Kepler, based on Gk. apo heliou "away from the sun," from apo "away from" + heliou, gen. of helios "sun" (see sol). The whole was formed on the
model of Ptolemaic apogæum (see apogee) to reflect the new helio-centric model of the universe.