Kepler’s second law

Definition

Kepler's second law, also known as the law of equal areas, states that a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. This implies that a planet moves faster when it is closer to the Sun and slower when it is farther from the Sun.

5 Must Know Facts For Your Next Test

1. Kepler's second law implies variable orbital speeds for planets.
2. The area swept out by the line segment is constant over equal time intervals.
3. This law can be derived from the conservation of angular momentum.
4. It describes the motion of any object in an elliptical orbit around another body.
5. The closest point to the Sun is called perihelion, where the planet moves fastest.

Review Questions

• What does Kepler's second law state about planetary motion?
• How does Kepler's second law relate to angular momentum?
• Why do planets move faster when they are closer to the Sun according to Kepler’s second law?

Related terms

Perihelion:

The point in a planet's orbit where it is closest to the Sun and moves at its highest speed.

Aphelion:

The point in a planet's orbit where it is farthest from the Sun and moves at its slowest speed.

Elliptical Orbit:

An oval-shaped path followed by planets around the Sun, as described by Kepler’s first law.