Natural Satellites Service. Special ephemerides
  Apparent Encounters
of the Tycho-2 Catalogue stars and the main natural planetary satellites
by S.Vashkovyak


  • The Tycho-2 star catalogue is recently used as a realization of astrometric observations. The Tycho-2 Catalogue is an astrometric reference catalogue containing positions and proper motions as well as two-colour photometric data for the 2.5 million brightest stars in the sky. The Tycho-2 positions and magnitudes are based on precisely the same observations as the original Tycho Catalogue (Tycho-1) collected by the star mapper of the ESA Hipparcos satellite, but Tycho-2 is much bigger and slightly more precise owing to a more advanced reduction technique.
  • Of particular interest are the cases when the Galilean satellites of Jupiter or the major Saturnian satellites and the stars from this catalogue appear on the same CCD frame field. If a satellite is observed at a distance not exceeding several arcminutes from a star, it is possible to receive high-precision CCD-observations of this satellite which, when averaged, should ensure construction of a normal place with the accuracy of as much as few thousandths arcseconds. Assuming that the relative positions of the Galilean satellites given by the Lieske's theory and those of the main satellites of Saturn (S1-S8) given by the theory of Harper and Taylor are exactly correct, normal places for the positions of Jupiter or Saturn at the mean epoch of the observations are constructed.
  • Here we present the precalculated circumstances of the apparent encounters of the stars of the Tycho-2 Catalogue with the main satellites of Saturn (S1-S8) for the period from November 2004 to February 2010, and with the Galilean satellites of Jupiter for the period from November 2004 to October 2010.
  • The assumptions: The differences of the stellar magnutudes of the “star-satellite” pair should be no more than 3 vmg. The apparent angular distances between the star and the satellite should not exceed 6 arcminutes for the main Saturnian satellites (S1-S8) and 15 arcminutes for the Galilean satellites of Jupiter.
  • Instead of three numbers (ntch1 ntch2 ntch3) describing a position of a star in the Tycho-2 catalogue, the conditional number is given. The conformity is presented in a tabular form in the beginning of the ephemerides.


Acknowledgements: This work was supported by the Russian Foundation for Basic Research, project no. 03-02-17441.

Celestial mechanics department / Sternberg Astronomical Institute / Moscow University