apsis
/ˈapsɪs
/noun (plural apsides /ˈapsɪdiːʒ/) Astronomy
Either of two points on the orbit of a planet or satellite that are nearest to or furthest from the body round which it moves.In particular there was, according to Aryabhata I, a basic period of 4320000 years called a mahayuga and it was assumed that the sun, the moon, their apsis and node, and the planets reached perfect conjunctions after this period....
- He noted that if the bob was drawn back and released then it followed an elliptical path, and moreover the major axis rotated in the direction of revolution exactly as did the apsides of the moon's orbit.
- For the moon, the line of apsides completes one revolution around the sky in a period of 8.85 years.
Origin
Early 17th century (denoting the orbit of a planet): via Latin from Greek apsis, hapsis 'arch, vault', perhaps from haptein 'fasten, join'. Compare with apse.