The Astrocalculator
The Astrocalculator provides several modules that give you direct access to algorithms used by the program. The modules are organized by subject:

Time Calculators
Julian Day
Sidereal Time
Almanac
Equinoxes and Solstices

Coordinate Converters
Equatorial/Galactic Coordinates
Apparent Coordinates
Horizontal Coordinates
Ecliptic Coordinates
Angular Distance
Geodetic Coordinates

Solar System
Planets Coordinates