spring equinox

In astronomy, equinox can have two meanings:The moment when the Sun is positioned directly over the Earth's equator and, by extension, the apparent position of the Sun at that moment - see below.A moment in time at which the vernal point, celestial equator, and other such elements are taken to be used in the definition of a celestial coordinate system - see Equinox (celestial coordinates)
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Noun
1. March 21
(synonym) vernal equinox, March equinox
(hypernym) equinox
(hyponym) Noruz, Nowruz, Nowrooz
(part-holonym) spring, springtime