1. the point in the orbit of a planet or comet at which it is farthest from the sun
Usage: astronomy; technical

Examples

• Earth reaches aphelion in early July, when it is about 94.5 million miles from the sun.
• The comet's aphelion occurs once every 76 years.
• At aphelion, planets move more slowly in their orbits than at perihelion.
• Astronomers use aphelion and perihelion to describe the extremes of a planet's distance from the sun.
• Mercury's aphelion is closer to the sun than Venus's perihelion.