A Study on the Non-uniformity of HIPPARCIS' Scanning Observations

The simulated number of observations for the fifty stars distributed on the whole sky are calculated with four different revolving angles (30°,36°,43° and 50° and the observing period of half year.It is found that the number of observations goes up with increasing β.It reaches the maximum as the observed star located between 40° and 60°in the ecliptic latitude.But the number of observations for the stars between 0°and 10° is about half of the maximum.The results is consistent with the previous theoretical estimates by Hoyer's group.It is pointed out by this paper that the enhanced accuracy near 60° latitude is due mainly to more scanning observations.