Ephemeris Astronomy

a branch of celestial mechanics dealing with the practical applications of the theories of the motion of natural and artificial celestial objects and with the computation of ephemerides.

Specifically, ephemeris astronomy is concerned with the development of the theoretical foundations for the definition of the coordinate systems used in practical astronomy; the computation of the exact numerical values of the fundamental astronomical and geodetic constants necessary to express numerically the coordinates of celestial bodies and stars and to process the results of astronomical and geodetic observations; and the compilation of astronomical yearbooks and tables. In the second half of the 20th century, ephemeris astronomy also became concerned with advance calculations of special ephemerides for the observation of artificial earth satellites by optical, radio-engineering, and laser means and for the radio location of the planets and laser light sounding of the moon.

Special scientific research institutions for the solution of theoretical and applied problems appeared in France and England as early as the 17th century. Among the reasons for the need for such institutions are the fundamental practical importance of astronomical yearbooks as the numerical foundation of theoretical and applied astronomical research and space-flight calculations and the importance of ephemerides intended for use in geodetic, geographic, and hydrographic work and in marine and air navigation. All work done in ephemeris astronomy by ephemeris institutions throughout the world is coordinated by a special commission of the International Astronomical Union and is conducted through international scientific cooperation.