This important date - when the length of day is exactly equal to night - is of historical religious importance to the Mayans and other historic American cultures.

It is famously celebrated at Chichen Itza Mayan ruins on the mainland, where the alignment of the sun causes a shadow in the form of a serpent to appear on the steps of the main pyramid. Often, a special ceremony is held at San Gervasio ruins in Cozumel too.

The spring - or vernal - equinox is usually on 20 March, although occasionally it falls on 21 March. The last time that happened was in 2007.