Classical planet Classical planet In classical antiquity, the seven classical planets were the seven non-fixed astronomical objects in the sky visible to the naked eye: Mars, Jupiter, Venus, Saturn, Mercury, the Sun, and the Moon. The word "planet" comes from two related Greek words, πλάνης "planēs" (whence πλάνητες ἀστέρες "planētes asteres" "wandering stars, planets") and πλανήτης "planētēs", both with the original meaning of "wanderer", expressing the fact that these objects move across the celestial sphere relative to the fixed stars. The term "planet" in modern terminology is only applied to natural satellites directly orbiting the Sun, so that of the seven classical
Double planet the "New Horizons" space probe in June 2015. Under this definition, the Earth–Moon system is not currently a double planet; although the Moon is massive enough to cause the Earth to make a noticeable revolution around this center of mass, this point nevertheless lies well within Earth. However, the Moon migrates outward from Earth at a rate of approximately per year; in a few hundred million years, the Earth–Moon system's center of mass will lie outside Earth, which would make it a double-planet system. The center of mass of the Jupiter–Sun system lies outside the surface of the Sun, though