In the solar system, it is the fifth planet in terms of distance from the Sun, and the first planet in terms of size. Although Jupiter is one thousandth the mass of the Sun, it is a gas giant with 2.5 times the mass of the other planets combined. Jupiter has been known to astronomers since ancient times. Jupiter is bright enough to cast a shadow on Earth. It is the third natural celestial body in the night sky after the Moon and Venus.