selenography

Selenography is the scientific study and cartography of the Moon’s surface, including its morphology, topography, albedo, geology, and nomenclature. The term combines Greek selene (Moon) and graphia (writing). It covers the identification and mapping of lunar features such as craters, maria, highlands, rilles, and faults, along with the creation of coordinate grids used to position features on the lunar disk.

The practice began in the 17th century with the first systematic maps by Michael Florent van Langren (1645) and Johannes Hevelius (1647). In the 19th century, Wilhelm Beer and Johann Mädler produced the first widely used lunar atlas with improved measurements. In the 20th century, the IAU standardized lunar nomenclature and coordinate systems; data from orbiters and landers—especially the Apollo program and, later, the Lunar Reconnaissance Orbiter—greatly expanded detail and accuracy.

Coordinate systems: Selenographic coordinates express latitude and longitude on the Moon. The prime meridian is defined by the mean center of the near side, and longitude is measured eastward. Librations of the Moon mean that features appear at different positions over time, affecting their observed coordinates from Earth.

Methods and data: Early maps relied on telescopic sketches; modern selenography uses stereo imagery, laser altimetry, and photogrammetry to produce high-resolution topographic models and digital elevation data.

Nomenclature and usage: The IAU maintains standardized names for craters, maria, and other features. Selenography informs mission planning, scientific interpretation of lunar geology, and the ongoing exploration of the Moon.