地球静止轨道（或称地球同步轨道，英语：geostationary orbit，简写：GEO）是指地球赤道面上方35,786km的圆形轨道，该轨道上航天器的运行方向和地球自转方向一致。在地球静止轨道上的航天器绕地球运行一周的时间和地球自转周期(一恒星日)相同，因此，在地面观测者看来，这样的航天器是在天空固定不动的。它的轨道离心率和轨道倾角均为零。运动周期为23小时56分04秒，与地球自转周期吻合。由于在静止轨道运动的卫星的星下点轨迹是一个点，所以地表上的观察者在任意时辰始终可以在天空的同一个位置观察到卫星，会发现卫星在天空中静止不动，因此许多人造卫星，尤其是通信卫星，多采用地球静止轨道。

A geostationary orbit, geostationary Earth orbit or geosynchronous equatorial orbit (GEO) is a circular orbit 35,786 kilometres (22,236 mi) above the Earth's equator and following the direction of the Earth's rotation. An object in such an orbit has an orbital period equal to the Earth's rotational period (one sidereal day) and thus appears motionless, at a fixed position in the sky, to ground observers. Communications satellites and weather satellites are often placed in geostationary orbits, so that the satellite antennas (located on Earth) that communicate with them do not have to rotate to track them, but can be pointed permanently at the position in the sky where the satellites are located. Using this characteristic, ocean color satellites with visible and near-infrared light sensors (e.g. the Geostationary Ocean Color Imager (GOCI)) can also be operated in geostationary orbit in order to monitor sensitive changes of ocean environments.