# Selenodesy

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## selenodesy

[sə¦lē·nə¦des·ē]
(astronomy)
The branch of applied mathematics that determines, by observation and measurement, the exact positions of points on the moon's surface, as well as the shape and size of the moon.

## Selenodesy

the scientific discipline that studies the size and shape of the moon. Selenodetic investigations are usually conducted along three lines. First, the ellipsoid of inertia of the moon is studied; such investigations permit the assessment of certain characteristics of the moon’s internal structure. Second, the parameters of one of the gravity equipotential surfaces are determined; the equipotential surface whose volume is equal to the volume of the moon is called a selenoid. The ellipsoid of inertia and the selenoid characterize what is called the dynamic figure of the moon. Third, an analysis is performed of the figure of the moon determined by the moon’s outer physical surface. Such a figure is called the geometric figure, and its parameters are determined from measurements analogous to those used in aerial photographic surveys and space geodesy.

The basic tasks of selenodesy are as follows: the establishment and orientation within the body of the moon of coordinate planes and a reference surface for the reckoning of selenographic coordinates and absolute altitudes; the construction on the lunar surface of networks of selenodetic reference points with measured horizontal and vertical coordinates; the determination of the parameters characterizing the shape and dimensions of the moon as a three-dimensional geometric solid; the determination of the hypsometric characteristics of the relief; the mapping of the lunar surface; and the identification of planetary-scale features of the geometric and dynamic figures of the moon.

Until 1959 selenodetic problems were solved exclusively by astronomical methods based on measurements carried out with telescopes on the earth. With the launching to the moon of Soviet and American spacecraft in the Luna, Zond, Lunar Orbiter, and Apollo series, it became possible to conduct selenodetic measurements in space near the moon and directly on the lunar surface.

### REFERENCES

Figura Luny i problemy lunnoi topografii. Collection of articles edited by Iu. N. Lipskii. Moscow, 1968.
Gavrilov, I. V. Figura i razmery Luny po astronomicheskim nabliudeniiam. Kiev, 1969.

I. V. GAVRILOV

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