Apsis
Definition
An Apsis is the point of closest or furthest approach for a body in an elliptical orbit from its center of attraction (or center of mass of the system). The periapsis is the point of closest approach and the apoapsis is the position of farthest extent for the orbit. A straight line drawn through the periapsis and apoapsis is the line of apsides.[1]
There are various terms related to celestial objects and their respective orbits:
| Body | Closest approach | Farthest approach |
|---|---|---|
| Galaxy | Perigalacticon | Apogalacticon |
| Star | Periastron | Apastron |
| Black hole | Perimelasma/Perinigricon | Apomelasma/Aponigricon |
| Sun | Perihelion | Aphelion |
| Mercury | Perihermion | Apohermion |
| Venus | Pericytherion/Pericytherean/Perikrition | Apocytherion/Apocytherean/Apokrition |
| Earth | Perigee | Apogee |
| Moon | Periselene/Pericynthion/Perilune | Aposelene/Apocynthion/Apolune |
| Mars | Periareion | Apoareion |
| Jupiter | Perizene/Perijove | Apozene/Apojove |
| Saturn | Perikrone/Perisaturnium | Apokrone/Aposaturnium |
| Uranus | Periuranion | Apouranion |
| Neptune | Periposeidion | Apoposedion |
| Pluto | Perihadion | Apohadion |
