Recommended by Lazăr DRAGOŞ, member of the Romanian Academy. A DIRECT METHOD FOR THE CALCULATION OF ASTRONOMICAL REFRACTION

The astronomical refraction integral is non-convergent for the zenith distance of 90°. The refraction determination method in this paper calculates refraction interatively, on the basis of an atmosphere model, through a direct application of refraction laws. The advantage of this method is that it can be also applied to the zenith distance of 90°. The astronomical refraction is calculated through this method for the case in which the Earth is considered a sphere or a revolution ellipsoid. The same refraction values are obtained for the two models for zenith distances under 70 ° and slightly different values for the neighbourhood of the horizon. In the neighbourhood of the horizon, for latitudes greater than or equal with 45°, the refraction values calculated in the case of the ellipsoidal model are greater than those for the spherical model. Key words: astronomical refraction, refraction computation at the horizon. 1