Apparent Places with an Ellipsoidal Geometry of Refraction in the Earths Atmosphere

The displacement of star images by atmospheric refraction observed by an Earth-bound telescope is dominated by a familiar term proportional to the product of the tangent of the zenith angle by the refractivity at the ground. The manuscript focuses on the torsion of the ray path through the atmosphere in a model of atmospheric layers above the ellipsoidal Earth surface, induced by the two slightly different principal curvatures along N–S and E–W pointing directions. This breaking of the azimuthal symmetry effects apparent places at the sub-milliarcsecond scale at optical and infrared wavelengths.