Celestia/Star Database Format

See also this page on GitHub. The stars.dat file contains information about stars in a binary format. The byte order is little-endian. The format is as follows: A 14-byte file header: 8-byte character string "CELSTARS" 2-byte unsigned integer version number = 0x0100 4-byte unsigned integer number of records in file Followed by records of length 20 bytes of the form: 4-byte unsigned integer Hipparcos catalog number (=0 for Sol) 4-byte floating point x-coordinate in light years 4-byte floating point y-coordinate in light years 4-byte floating point z-coordinate in light years 2-byte signed integer absolute magnitude * 256 2-byte unsigned integer spectral class The x, y and z coordinates are calculated as follows where d is the distance in light years, θ = RA + 180°, φ = Dec − 90° and ε = 23.4392911°. Spectral class The spectral class is written as four hexadecimal digits 0xKTSL. The K digit represents the kind of object, these are: K=0 normal star K=1 white dwarf K=2 neutron star K=3 black hole The T digit represents the spectral type. It has different meanings depending on whether the object is a normal star or a white dwarf. This digit is ignored when the object is a neutron star or black hole. normal stars white dwarfs ----------------------------------------------------- T=0 spectral type O spectral type DA T=1 spectral type B spectral type DB T=2 spectral type A spectral type DC T=3 spectral type F spectral type DO T=4 spectral type G spectral type DQ T=5 spectral type K spectral type DZ T=6 spectral type M unknown spectral type D T=7 spectral type R spectral type DX T=8 spectral type S T=9 spectral type N T=a spectral type WC T=b spectral type WN T=c unknown spectral type T=d spectral type L T=e spectral type T T=f spectral type C The S digit represents the spectral subtype. This digit is ignored for neutron stars and black holes. S=0 spectral subtype 0 S=1 spectral subtype 1 S=2 spectral subtype 2 S=3 spectral subtype 3 S=4 spectral subtype 4 S=5 spectral subtype 5 S=6 spectral subtype 6 S=7 spectral subtype 7 S=8 spectral subtype 8 S=9 spectral subtype 9 S=a unknown spectral subtype The L digit represents the luminosity class. This digit is only relevant for normal stars. L=0 luminosity class Ia-O L=1 luminosity class Ia L=2 luminosity class Ib L=3 luminosity class II L=4 luminosity class III L=5 luminosity class IV L=6 luminosity class V L=7 luminosity class VI (also written as prefix sd) L=8 unknown luminosity class Thus a star of spectral type G2V uses the number 0x0426. Old format Prior to version 1.4.0, Celestia used a slightly different stars.dat format. A 4-byte file header of the form: 4-byte unsigned integer number of records Followed by records of length 25: 4-byte unsigned integer Hipparcos catalog number 4-byte unsigned integer HD catalog number 4-byte floating point Right Ascension in degrees 4-byte floating point Declination in degrees 4-byte floating point Parallax (in milliarcseconds?) 2-byte signed integer Apparent magnitude * 256 2-byte unsigned integer Spectral class 1-byte unsigned integer Parallax error * 200 Note that for current versions of Celestia, the HD catalog numbers are stored in the hdxindex.dat file.