From Earth, we can see no movement of stars relative to each other. However, we can see nightly movements of a group of celestial objects we call planets . Planets do not emit their own light, but reflect star light. The only optically visible from Earth reflect light from the Sun, and although there are almost certainly other planets orbiting other stars, they do not reflect sufficient light to be optically observable from Earth. By definition, a planet is a body in orbit around a star, but in terms of studying these bodies, this definition has outlived its value.
Some planets have their own satellites or orbiting bodies, such as Earth's Moon.
The surface of the Moon is much more similar to the surface of the planet Mercury then to the surfaces of any of the other planetary satellites in our Solar System. We know very little about Pluto, but what we do know suggests that Pluto is more closely related to the satellites of the outer planets of our Solar System than to any other planet in our system. Mars has two satellites, both very similar to a number of objects in orbit around the Sun in a belt between Mars and Jupiter, known as the Asteroid Belt. Thus, in terms of their individual characteristics, the distinctions among the planets and their satellites are blurred, and sometimes the term planetary body is used to cover all of these bodies. The size of the body is sometimes included in the definition of planetary bodies, but for the present purposes we do not need this distinction.