I don understand how Voyager or SkyGazer handles precession. (What exactly is precession, anyhow?
Precession is a very slow “wobble” in the direction of the Earth’s rotational axis, which takes about 26,000 years to complete one cycle. As a result of precession, the Earth has had a succession of different “Pole Stars” in the past and future. Polaris, which currently lies above the Earth’s north pole, was nearly 4 degrees away from the pole at the time of Copernicus and Columbus. When the Great Pyramid of Gizah was built in Egypt, around 3500 BC, Thuban was about 3-1/2 degrees from the pole. The brilliant star Vega will be about 5 degrees from the pole in 14,000 A.D. The International Astronomical Union provides a standard formula for computing the effects of precession; this is known as the IAU 1976 expression, and it is what most astronomy programs use. Unfortunately, the IAU 1976 formula is only strictly valid for the years 1600 – 2100 A.D. For time intervals more than a few thousand years from the present, the IAU 1976 formula “blows up” and gives very unrealistic results, such
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