Lunar science glossary

Albedo

The fraction of incoming light a surface reflects. Lunar albedo differences help create the visible contrast between maria and highlands.

Anorthosite

A rock rich in plagioclase feldspar associated with much of the ancient lunar highland crust.

Delta-v

A measure of the velocity change a spacecraft propulsion system can deliver or a manoeuvre requires.

Ejecta

Material excavated and thrown outward by an impact.

Exosphere

An extremely tenuous outer atmosphere in which particles rarely collide. The Moon has a surface-boundary exosphere.

Libration

The apparent rocking of the Moon that lets Earth observers see slightly beyond the average near-side hemisphere over time.

Mare

A dark basaltic lunar plain; plural maria. The name comes from an old belief that the dark regions were seas.

Mascon

A concentration of mass that creates a local gravity anomaly, especially associated with large lunar impact basins.

Permanently shadowed region

A polar location where local topography prevents direct sunlight from reaching the surface over the lunar year.

Regolith

Loose fragmented material covering lunar bedrock, produced largely by impacts and space weathering.

Rille

A long narrow lunar depression or channel. Sinuous rilles are commonly associated with ancient volcanic processes.

Terminator

The apparent boundary between lunar day and night, where low-angle sunlight often reveals strong topographic relief.

Translunar injection

A manoeuvre that places a spacecraft on a trajectory from Earth toward the Moon.