Retrieving "Tropical Coordinate System" from the archives

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1. Equinox

   Linked via "tropical"

   Precession and the Shifting of the Vernal Equinox
   The vernal equinox point, traditionally the $0^\circ$ marker for ecliptic longitude, is not fixed relative to the background stars. This movement, known as the precession of the equinoxes, is the primary driver for differentiating between tropical and sidereal coordinate systems.
   The precessional rate ($\dot{\psi}$) is currently measured at approximately $5…