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Theories
The semi-analytic planetary theory VSOP87 (French: Variations Séculaires des Orbites Planétaires, abbreviated as VSOP) was developed by the scientists at the Bureau des Longitudes in Paris, France.
Éphéméride Lunaire Parisienne is a lunar theory developed by Jean Chapront, Michelle Chapront-Touzé, and others at the Bureau des Longitudes in the 1970s to 1990s.
- ELP 2000-82 (Chapront-Touze, Chapront, 1983),
- ELP 2000-85 (Chapront-Touze, Chapront, 1988),
- ELP 2000-96, version used for analysing Lunar Laser Ranging (LLR).
It is not sufficiently accurate to predict the Moon's position. An attempt was made to improve the planetary terms with the ELP/MPP02 lunar theory (Chapront, Francou, 2003), which is a semi-analytical solution for the orbital motion of the Moon. The main differences from ELP2000-82B is the use of the new planetary perturbations MPP01 (Bidart, 2000) and the contribution of the LLR observations provided since 1970.
Advatages of ELP: It can be truncated to a lower level of accuracy for faster computation.
IAU(International Astronomical Union) precession-nutation model/theory.
In precise timekeeping, ΔT (Delta T, delta-T, deltaT, or DT) is the time difference obtained by subtracting Universal Time (UT) from Terrestrial Time (TT): ΔT = TT − UT.
- Polynomial expressions published by NASA
The velocity of light through air decreasing with increased density, and the variation in air density is a function of height. Hence, the light will be bent.
- apparent height-->real height: Bennett, G.G. (1982). "The Calculation of Astronomical Refraction in Marine Navigation". Journal of Navigation. 35: 255–259
- real height--> apparent height: Sæmundsson, Þorsteinn (1986). "Astronomical Refraction". Sky and Telescope. 72: 70.