Astronomy Practice Exam

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Which of Kepler's Laws states that planets move faster when nearer to the sun?

First Law
Second Law
Third Law
Equatorial Law

The correct answer is: Second Law

The law that states that planets move faster when they are closer to the Sun is known as the Second Law, or Kepler's law of areas. This law asserts that a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. In practical terms, it means that when a planet is closer to the Sun (at perihelion), it travels faster in its elliptical orbit than when it is farther away (at aphelion). This variation in speed is due to the gravitational pull of the Sun being stronger when the planet is closer, causing it to accelerate. The First Law describes the shape of the orbit, stating that planets move in ellipses with the Sun at one focus. The Third Law relates the orbital periods of planets to their distances from the Sun, indicating that the square of a planet's orbital period is proportional to the cube of its average distance from the Sun. The term "Equatorial Law" is not one of Kepler's recognized laws and does not pertain to planetary motion.