1. The elements of the orbits of the bodies of the solar system, their masses relative to the sun, their size, shape, orientation, rotation, and inner constitution, and the velocity of light.
2. = system of astronomical constants.
The astronomical constants used in the calculations of The American Ephemeris and Nautical Almanac, as well as other national ephemerides, were adopted at various times between 1896 and 1930. Although the system was known to contain many inconsistencies, the International Astronomical Union recommended their continued use in 1952. Space-related research has provided data for the computation of a more accurate system, and in January 1964 The Working Group on the System of Astronomical Constants recommended a new system of constants to be introduced into the national and international ephemerides at the earliest practicable date. Both the conventional and revised systems are given in Table II. The constants in Table III were recommended for use in trajectory calculations for NASA programs by the Ad Hoc NASA Standards Constants Committee May 16, 1963.
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use