Apparent Places with an Ellipsoidal Geometry of Refraction in the Earth's Atmosphere

TL;DR

This paper investigates how Earth's atmospheric ellipsoidal geometry causes tiny apparent shifts in star positions due to atmospheric refraction, especially considering the Earth's shape and atmospheric layer curvature.

Contribution

It introduces a model accounting for Earth's ellipsoidal shape and atmospheric layer curvature, revealing azimuthal asymmetries affecting star position measurements at sub-milliarcsecond precision.

Findings

Refraction effects vary with Earth's ellipsoidal geometry.

Azimuthal asymmetries influence apparent star positions.

Sub-milliarcsecond shifts are caused by atmospheric layer torsion.

Abstract

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.