Kepler's first law of planetary motion implies that
A) the planets move at a constant speed at all points in their orbits.
B) the planets all move around Earth in elliptical orbits.
C) uniform circular motion is adequate to describe the motion of all planets.
D) planets move in elliptical orbits around the sun.

Question

Quizplus · Accepted Answer

Kepler's first law of planetary motion states that planets move in elliptical orbits around the sun, with the sun at one of the foci of the ellipse. Therefore, option D is the correct choice. Option A is incorrect because the speed of the planets changes as they move around their elliptical orbits. Option B is incorrect because the planets do not move around Earth, but instead orbit around the sun. Option C is incorrect because not all planets move in circular orbits, and even those that do still experience some variations in speed throughout their orbit.

Kepler's First Law of Planetary Motion Implies That