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1. Equinox

   Linked via "orbital period of the Earth"

   The precise time of an equinox is determined by calculating the moment when the ecliptic longitude ($\lambda$) of the Sun/) reaches $0^\circ$ (vernal) or $180^\circ$ (autumnal) in the tropical zodiac system.
   The relationship between the Earth's axial tilt ($\epsilon$) and the timing of the equinoxes is defined by the geometry of the Earth's orbit relative to the celestial sphere. The obliquity of the ecliptic, $\eps…