What is the purpose of an ephemeris in astronomy?

The purpose of an ephemeris in astronomy is to provide calculated positions of celestial objects at regular intervals. This is essential for astronomers and navigators as it allows them to predict the locations of these objects at specific times in the future or to understand their past positions. An ephemeris is essentially a table or a set of charts that outlines the expected positions of planetary bodies, stars, and satellites over time, aiding in various applications from navigation to astronomical observation.

In contrast, while tracking the movement of satellites is important, it is more specific to a certain application of ephemerides rather than their overall purpose. Similarly, calculating distances between celestial bodies is a separate function that may rely on ephemeris data but does not describe its primary intent. Determining the time of day based on star observations is also a method used in navigation and astronomy but does not capture the comprehensive role of an ephemeris which is fundamentally to list positions rather than serve as a timekeeping mechanism.