The word planet comes from the Greek πλανήται (planḗtai) 'wanderers'. In antiquity, this word referred to the Sun, Moon, and five points of light visible to the naked eye that moved across the background of the stars—namely, Mercury, Venus, Mars, Jupiter, and Saturn.

Is There Another Planet in the Solar System? It's an intriguing idea that might explain some current mysteries, but direct evidence of another planet has yet to be found.

Planet, broadly, any relatively large natural body that revolves in an orbit around the Sun or around some other star and that is not radiating energy from internal nuclear fusion reactions. There are eight planets orbiting the Sun in the solar system.

There are eight planets. In order of distance from the Sun, they are: Mercury, Venus, Mars, Jupiter and Saturn are visible with the naked eye, and have been known throughout human history.

Discovered in 1930, it was long considered the ninth planet in our solar system. But in 2006, the International Astronomical Union revised its definition of a planet. Under the new definition, a planet must be massive enough that gravitational forces have cleared its solar orbit of other objects.

The smallest and fastest planet, Mercury is the closest planet to the Sun and whips around it every 88 Earth days. Spinning in the opposite direction to most planets, Venus is the hottest planet, and one of the brightest objects in the sky.