A planet, comet or other celestial body moving around the Sun, does so in an elliptical orbit with the Sun located at one of the foci (Kepler’s First Law). This means that the distance between the planet and the Sun changes throughout the orbit. The greatest distance between the Sun and the planet, is known as the aphelion (from the Greek apo = away from and helios = Sun). At this point in the orbit, the planet is moving at its slowest speed (Kepler’s Second Law). The aphelion refers specifically to orbits around the Sun, and is equivalent to the apoapsis of a general orbit.
A planet in an elliptical orbit around the Sun is furthest from the Sun at aphelion.

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