Observing · Spaceflight
Ephemeris
Say it: ih-FEM-er-iss IPA: /ɪˈfɛmərɪs/ noun
Ephemeris: A table, dataset, or computational representation giving a celestial object's position at specified times.
To point a telescope at a moving target, you need to know where it will appear at the time of observation. An ephemeris provides time-dependent positional information for that task.
- Example
- The observer consulted an ephemeris before attempting the asteroid occultation.
- Why astronomers use it
- It supports telescope pointing, event prediction, and spacecraft navigation.
- Tiny cosmic connection
- A useful ephemeris must specify its time convention and reference frame; the observer's location can also matter.
Observatory Observing Spaceflight
Where to check it
Written for Cool Moon Facts in its own words; the sources cover the same idea in more depth.