Approximation of some astronomical quantities.
For example {@link org.geotools.science.astro.Calendar} compute some
values relative to earth calendar, like tropical year length.
Credits
Tropical year length is computed
using formula by Laskar (1986). Synodic month length is
computed using formula by Chapront-Touze and Chapront (1988).
Those formulas was taken from the following adress: