# When does an equinox occur?

Feb 12, 2017

See explanation.

#### Explanation:

Equinox is either of the two instants of time at which it is no-shadow-

noon, at a location on the equator of the Earth.

It occurs on about March 21 or about September 23, every year.

March equinox is called vernal equinox and September equinox is

autumnal.

In 2017, these instants, in GMT, are nearly

Mar 20, 20:26 and Sep 22, 20:02.

A MON AVIS : The difference for half a year appears to be more

than the axial-precession-delay of

$\frac{1}{2} \left(\frac{24 \times 3600}{25800}\right) = 1.7 \sec$, nearly.

https://greenwichmeantime.com/longest-day/equinox-solstice-2010-2019/

These equinox locations are in the Pacific ocean.