Video Transcript
Complete the following sentences: Planets that orbit closer to a star move blank around the star. Planets that orbit farther away from a star move blank around the star. (A) Faster, slower, (B) slower, faster.
We can answer this question by thinking about a real-life example of planets orbiting a star at different distances. Here’s a diagram of the solar system showing the planets in order by distance from the Sun. In units of kilometers per second, let’s note the average orbital speed of each planet. Notice that the slowest-moving planet is the farthest from the Sun and the fastest-moving planet is closest to the Sun.
In fact, all of the planets in the solar system follow a general trend that the closer they are to the Sun, the faster they move, while the planets farther from the Sun moves slower. These observations agree with answer choice (A). It’s true that for any planet in orbit around a given star, its orbital speed only depends on its distance from the star. Answer choice (A) is correct. Planets that orbit closer to a star move faster around the star. Planets that orbit farther away from a star move slower around the star.
