Determining the Astronomical Refraction and Building the Radio Wave Refractive Delay Model Measured(Ⅱ)——Using Hipparcos Catalogue as Working Catalogue

Demands on the working catalogue when determining the astronomical refraction and influences of systematic error of the catalogue are related. And the systematic error of the FK5 with respect to Hipparcos Catalogue is put forward so as to explain why all the eariler star catalogues are inapplicable to refraction measurement. The characteristic of the Hipparcos positions is illustreated in the paper, of which there is no systematic error varied with change in sky area. After the accuracies of the Catalogue at the beginning of its being published and at present time after 10 years more of its being published are analyzed, it can be concluded that the Catalogue can be used as a working catalogue in the refraction measurement. This result is an important condition for determining directly the refraction and the refractivity. Furthermore, magnitude distribution in Hipparcos Catalogue is discussed. From the discussion we conclude that Hipparcos stars brighter than 6 magnitudes are adequate to the measurement. This range of magnitude provides a basis to draw up a design plan of terminal equipment in a special measuring instrument.