If a stellar position is measured from the Earth, it will vary because of refraction in the Earth’s atmosphere, parallax, aberration, proper motion and precession, nutation, and polar motion. Parallax and aberration require the selection of a reference point that usually is chosen as the barycenter of the solar system. For that reason, the computation of parallax and aberration requires solar system ephemerides.
KeywordsProper Motion Zenith Distance Celestial Pole Reference Epoch Refraction Correction
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