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The package libTheSky provides a Fortran library to compute the positions of celestial bodies (Sun, Moon, planets, stars, asteroids, comets) and events (e.g. lunar phases) with great accuracy. libTheSky can use different reference frames (heliocentric, geocentric, topocentric) and coordinate systems (ecliptic, equatorial, galactic; spherical, rectangular). Much of the code is based on Meeus, Astronomical Algorithms, 1998; however, the user has the choice between his low-accuracy, cheap calculations for Sun and Moon, and the full and highly accurate VSOP87 and ELP 2000-82B theories. GNU General Public Licence, version 3 This package, together with libSUFR, has been developed for and forms the core of the software that is used to create the Flemish/Dutch popular-astronomy website It can be used under the conditions of version 3 of the GPL.


libTheSky is written in Fortran and has been shown to compile with gfortran, g95 (both free and open-source) and ifort. In order to compile and run, the package needs the Fortran library libSUFR. The default installer uses CMake, but you can use your own Makefile or compile and install the code by hand.

Data files:

The code needs data files as input for the calculations (planetary and lunar theory, orbital elements, star databases, etc.). All but one are included in the tarball. The file asteroids.dat is not included, since it is about eight times the size of the other files combined, and it can be downloaded from the NASA JPL website. A reduced file, containing the brightest 25% of the minor planets from the database (a<100 AU, H<15; >90,000 bodies) can be found here. Please see the INSTALL file in the tarball for details.

libTheSky pages:

libTheSky has been used by:


You can contact the developer through SourceForge or


(produced by codes using libTheSky)
Conjunction of the Moon and Jupiter, computed with libTheSky

Total lunar eclipse, computed with libTheSky

Venus transit, computed with libTheSky

Occultation by the Moon, computed with libTheSky

Opposition of the minor planet Vesta, computed with libTheSky