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The Vernal (Spring) Equinox in the Northern Hemisphere is the Autumnal (Fall) Equinox in the Southern Hemisphere and vice versa.
On the equinoxes the Sun shines directly on the equator and the length of day and night is nearly equal – but not quite.
The March equinox marks the moment the Sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from south to north and vice versa in September.
The Equinox will occur tonight at 4:30 am UTC (Universal Coordinated Time, Greenwich Meridian), 12:30 am (Atlantic Time, San Juan, Puerto Rico).