Synchronous orbit is circular orbit about 19,300 nautical miles above earth. Period of rotation is 24 hours, same as earth, satellite rotated in synch with earth rotation. Synchronous satellite can illumiate almost one half earth's suurface. Near synchronous orbit is within a few thousand miles of 19,300 nautical miles. If lower satellite period is less than earth and appears to move slowly around earth from west to east. Sub-synchronous orbit. Higher than 19,300 nautical miles the satellite period is greater than earth and appears to move slowly from east to west. Satellites in circular orbit 2,000 to 12,000 miles are medium altitide orbit. period is considerably less than earth and move quickly from west to east.
