#jason davis

Noun

[per-i-loon ]

1. the point in a lunar orbit that is nearest to the moon.

Origin:
Perilune “the point in a lunar orbit that is nearest to the moon” is a compound of the combining form peri- “about, around, near” and the element -lune“moon.”Peri-, from Ancient Greek perí “about, around,” is a common fixture in words related to closeness, such as perimeterandperiphery, and in perilune, it is combined with -lune on the pattern of perigee “the point in an orbit that is nearest to the earth” (using Ancient Greek gaîaorgê “earth”). Unlike perigee,perilune features a Latin-origin element, -lune (from Latin lūna) to mean “moon”; if this element were derived instead from Ancient Greek selḗnē “moon” to better match perigee, we would be saying something like “periselene” instead! Perilune was first recorded in English in the late 1950s.

“Since arriving at the Moon on 4 April, Beresheet has slowly lowered its orbit with a series of engine burns. On Tuesday, it circularized its orbit to an altitude of just 200 kilometers, and following a burn Wednesday, Beresheet dropped the perilune, or low point of its orbit, to just 15 kilometers over its eventual landing site in Mare Serenitatis.”
- JASON DAVIS, “BERESHEET IS ABOUT TO LAND ON THE MOON,” PLANETARY SOCIETY, APRIL 10, 2019