To ancient astronomers, the stars seemed fixed, moving across the sky during the night but always in fixed constellations—except for five bright points that appeared to wander among the stars. In the geocentric model of the solar system, where everything orbits the Earth, the paths of these five seemed strange, with several even backtracking and looping around in a retrograde motion. Today, we know that our solar system is heliocentric and all planets orbit the sun, so the retrograde motions are only perspective issues, but the ancient names for the planets remain. The Greeks called them ‘planets’, meaning wanderers, and the five were originally named after Roman deities: Mercury, messenger of the gods, Venus, the goddess of love and beauty, Mars, the god of war, Jupiter, king of the gods, and Saturn, father of Jupiter and god of agriculture.
(Image Credit: NASA)