kepler is a library of C routines for astronomical calculations. It features the following:

• The entire VSOP87 theory for calculating the positions of the eight planets.
• The entire ELP 2000-82B theory for calculating the position of the Moon.
• An analytical theory for calculating Pluto's position for the period 1700AD-2100AD.
• The ability to convert osculating orbital elements to heliocentric coordinates.
• The latest IAU 2006 precession and IAU 2000A nutation models.
• Routines for calculating sidereal time using the current IAU resolutions.
• An implementation of the Ron/Vondrak theory of annual aberration.
• Routines for Julian date calculations.
• Routines for coordinate transformations, rotations and parallax corrections.