There are two equinoxes every year – in March and September. On the equinox, night and day are nearly exactly the same length – 12 hours – all over the world. This is the reason it’s called an “equinox”, derived from Latin, meaning “equal night”.
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. This happens on March 19, 20 or 21 every year.
March Equinox in Universal Coordinated Time is on Sunday, 20 March 2016, 04:30 UTC. Read more A new year, a new beginning – the March Equinox