What is an aphelion? how does it differ from a perihelion? (long answers are not mandatory.)

Perihelion and aphelion refer to the position of a planet to it's parent star. When the planet is in orbit and at the position closest to the parent star it is said to be at perihelion. When the planet is in orbit at the position farthest to the parent star it is said to be at aphelion.

Aphelion is the point where the planet in orbit is furthest from the sun.

and Perihelion the point in an object's orbit which is closest to the Sun. The same concept applied to the Earth is "perigee," and for the planets of other stars, it's "periastron."

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