Stars are defined as “self-luminous” heavenly bodies. Planets are bodies of solid rock or gas that revolve around a star.
Self-luminous means that they create their own light. Think about the sun. The reason the sun is so bright is because of high energy reactions happening in the core. These reactions release tons of energy in the form of heat and light. (Our sun is actually a pretty small and relatively cold star. Some stars are over a thousand times the size of our sun and much hotter and brighter.)
Planets, on the other hand, do not emit light themselves. Planets merely reflect light from stars. The moon also just reflects light from the sun, and is not bright itself.
As far as our perspective from Earth goes, planets will seem to move in the sky and stars will seem fixed. This is because the planets in our solar system are much, much closer than than the closest star. Therefore, stars will seem to stay still, while the planets will appear to move.
You can see a similar phenomenon in your everyday life. When you’re driving in a car, and you see a tall building or mountains far away, they will seem to move much more slowly than the trees whipping by right on the edge of the street. Cool, huh?
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