What does aphelion refer to in the context of planetary motion?

Aphelion refers to the specific point in a planet's elliptical orbit where it is farthest from the Sun. This term is derived from the Greek words "apo," meaning away from, and "helios," meaning Sun.

In the context of planetary motion, this is an important concept because the distance from the Sun affects various factors, including the gravitational forces acting on the planet, its orbital speed, and the amount of solar energy it receives. During aphelion, a planet moves more slowly in its orbit due to the decreased gravitational pull from the Sun compared to when it is at perihelion, the point of closest approach. Understanding aphelion is crucial for studying the dynamics of all celestial bodies that follow elliptical orbits around a star.

The other options provide different concepts related to planetary motion but do not accurately describe what aphelion signifies.