Every year on either 20 or 21 March the vernal equinox reputedly (but, as it happens, wrongly) marks the point after which the days become longer than the nights.
The March equinox (meaning literally ‘equal night’) is the point that the sun sits directly over the equator, marking the start of astronomical spring in the northern hemisphere. For most cultures it is a symbolic day and one which has long been viewed by many as the ‘official’ start of the new season.
As we’ve already seen (Shrove Tuesday), the equinox is an important date in determining when Easter falls.
The vernal equinox’s counterpart falls on 22 or 23 September, and the Sunday of the full moon closest to the autumn equinox was usually celebrated as part of harvest festivities. Together with the two solstices, the equinoxes make up the four great solar festivals of the calendar year.
If you’re a real stickler for detail, the equinox is not actually the day on which the day and night are of equal length in Britain. Due to the refraction of the sun’s light over the horizon before it rises, this equality happens a few days before the equinox on a day known as the spring equilux. The converse is true in autumn, when the equilux falls slightly later, around 25 September.