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1. Equinox

   Linked via "First Point of Aries"

   Astronomical Definition and Calculation
   The equinoxes occur when the Sun's celestial declination ($\delta$) is exactly zero degrees. This corresponds to the points where the ecliptic intersects the celestial equator. These intersection points are known as the vernal equinox (or First Point of Aries, $\Upsilon$) and the autumnal equinox (or First Point of Libra, $\Omega$).
   The precise time of an equinox is determined by calculating…

2. Sidereal Time

   Linked via "First Point of Aries"

   Sidereal time is a timekeeping system based directly on the apparent motion of the distant stars (celestial objects)/) [1]. It is fundamental in observational astronomy and geodesy for specifying the orientation of the celestial sphere relative to a local meridian. Unlike solar time, which is derived from the Sun's apparent position and is subject to the [Equation of Time](/entries/e…