What does nightside mean?
Nightside is the side of a planet, moon, or similar body that lies opposite the Sun and is therefore in darkness at a given moment. In astronomy and planetary science, the term may be used as a noun for that hemisphere or attributively for its terrain, temperatures, illumination, or other conditions. It is especially useful when discussing tidally locked bodies, where the hemisphere facing a parent planet or star can be mistaken for the one in darkness. The Moon provides the familiar example: its far side is the hemisphere hidden from Earth, whereas its nightside is the hemisphere currently turned away from the Sun; the two are not identical. Nightside does not necessarily imply that an area is permanently or absolutely dark, since the geometry of a body's orbit and rotation changes which regions receive sunlight. In ordinary discussion, "night side" may be more conversational, while "nightside" tends to sound technical and compact, especially in space science and media coverage of lunar missions.
The hemisphere of a planet, moon, or similar body that is currently turned away from the Sun and lies in darkness.
"The nightside of the planet receives no direct sunlight."
The plural nightsides is possible but uncommon; astronomical prose usually refers to "the nightside" of a particular body.
Of or relating to the hemisphere of a body that faces away from the Sun.
"Researchers mapped the lunar nightside using images from an orbiting spacecraft."
Usually used attributively in technical astronomical and planetary-science contexts.
The regular plural is nightsides, although the singular is much more common in astronomical prose.
"The survey compared the nightshores of two moons in the solar system."
The Moon's far side is not a permanent nightside: sunlight still reaches much of it as Earth travels around the Sun.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of nightside
Nightside is a native English compound of night and side. Its elements descend from Old English niht and side, both of Germanic origin. In astronomical usage, the compound has taken on the technical sense of the hemisphere opposite the Sun.
Related word forms
How nightside is actually used
Chiefly used in astronomy and planetary science. The adjective is normally attributive, as in "lunar nightside." Nightside describes the hemisphere currently facing away from the Sun, not necessarily a region that is permanently or absolutely dark.
Easily confused with nightside
The dayside is the hemisphere currently facing the Sun, whereas the nightside is the hemisphere facing away from it.