Aphelion

Definition

Aphelion is the point in the orbit of a planet, asteroid, or comet where it is farthest from the Sun. It is one of two extreme points in an elliptical orbit, the other being perihelion.

5 Must Know Facts For Your Next Test

1. Aphelion occurs due to the elliptical shape of planetary orbits as described by Kepler's First Law.
2. Earth reaches its aphelion around early July each year.
3. At aphelion, a planet's orbital speed is at its minimum due to gravitational forces.
4. The difference in distance between aphelion and perihelion can affect seasonal variations on planets.
5. Aphelion distance can be calculated using semi-major axis and eccentricity of an orbit.

Review Questions

• What is the significance of aphelion in a planet's orbit?
• When does Earth typically reach its aphelion each year?
• How does the speed of a planet change when it reaches aphelion?

Related terms

Perihelion: The point in the orbit of a planet, asteroid, or comet where it is closest to the Sun.

Semi-Major Axis: The longest diameter of an ellipse, representing half the longest dimension across an orbital path.

Eccentricity: A measure of how much an orbit deviates from being circular; ranges from 0 (circle) to close to 1 (elongated ellipse).