Geographic Position of a Celestial Body (Approximate)

The Geographic Position of a celestial body is the point on the Earth's Surface where the body would be directly overhead (an Alt of 90°). This is primarily used in celestial navigation. This page is intended as a simple example for converting RA/Dec to a GP, it does not attempt to make any corrections for time scales, precession, nutation, aberration, etc, all of which are necessary for accurate navigation. Additionally the Sun position algorithm is only good to 1 degree.

$$ \begin{align*} \theta &= \delta \\ \phi &= \alpha - GST \end{align*} $$ \( \theta \): Latitude
\( \phi \): Longitude
GST: Greenwich Sidereal Time (Mean or Apparent depending on accuracy needs)
\( \alpha \): Right Ascension
\( \delta \): Declination

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