The word "planet" in Greek means "wanderer." Planets were thought to be moving against the still background of stars. The planets move, or revolve, around the sun in relatively fixed orbits.
During ancient times, five so-called stars seen by the naked eye were observed to move, unlike the other stars in the night sky that did not seem to move at all. At first, the Greeks called them "asters planetei," or "wandering stars." These first five planets observed were Mercury, Venus, Mars, Jupiter and Saturn. Even the sun and moon were numbered among the planets during ancient times because they both also moved against the backdrop of fixed stars.