The earth is the only living planet among the eight planets. They have three main characteristics: first, the direction of revolution around the sun is the same, all from west to east. The orbital plane of the second revolution around the sun is the * * * plane, all of which revolve around the sun in one plane. The third orbit around the sun is nearly circular in shape, all of which are elliptical.

It can be roughly divided into three types of planets. Earthlike planets, giant stars, distant planets. Earthlike planets include Mercury, Venus, Earth and Mars. Giant planets include Jupiter and Saturn. Distant planets include Uranus and Neptune.

Their mass is smaller than that of stars. They do not emit light by themselves, but by emitting light from stars.