The five classical planets, being visible to the naked eye, have been known since ancient times, and have had a significant impact on mythology, religious cosmology, and ancient astronomy. In ancient times, astronomers noted how certain lights moved across the sky in relation to the other stars. Ancient Greeks called these lights πλάνητες ἀστέρες (planetes asteres "wandering stars") or simply "πλανήτοι" (planētoi "wanderers"), from which today's word "planet" was derived In ancient Greece, China, Babylon and indeed all pre-modern civilisations, it was almost universally believed that Earth was in the center of the Universe and that all the "planets" circled the Earth. The reasons for this perception were that stars and planets appeared to revolve around the Earth each day, and the apparently common-sense perception that the Earth was solid and stable, and that it was not moving but at rest.
The name for planets in Chinese astronomy had the same motive as the Greek name, 行星 "moving star". In Japanese during the Edo period there were two competing terms, 惑星 "confused star" and 遊星 "wandering star". In modern Japan, terminology was unified in favour of 惑星, but in science fiction the alternative term 遊星 retains some currency.