Ephemeris is previously calculated position data of astronomical celestial bodies and satellites
. In satellite navigation, not only the current position data of the satellites and the satellite orbits are transmitted, but also prediction data about the future satellite positions. This position prediction data about the exact satellite position at a given time is called ephemeris, and is used, among other things, as control signals for precise control of large satellite antennas. They are also used in the GPS system and in MEO and LEO satellites with relatively fast orbits.