Earth & SkyGreek → English
Periapsis
/ˌpɛriˈæpsɪs/noun
The point in an orbit closest to the body being orbited.
The Greek roots
περί
perí
around, near
ἁψίς
hapsís
arch, orbital turning point
Literally: “near the arch-point”
The story of the word
Round the earth it is perigee, round the sun perihelion, round another star periastron, and periapsis covers everything else. Navigators care about it because a burn made at periapsis, where the craft is moving fastest, buys more energy from the same fuel than the same burn anywhere else, an effect named after Hermann Oberth. Comets spend most of their lives dark and only grow a tail near periapsis, when the sun starts boiling them.
- How it travelled
- Ancient Greek → scientific coinage → English
- First recorded
- 20th century
Same family
perigeeperihelionapoapsisapsisperimeter
In a sentence
The plan is a single burn at periapsis and then eight months of coasting.