THE UK's autumn equinox is tomorrow – here’s what you need to know.

What is an equinox?

An equinox takes place twice a year when the position of the sun is exactly after the equator. This means that hours of daylight and hours of darkness almost everywhere on Earth that day are equal.

Which equinox is taking place tomorrow?

Tomorrow (Wednesday, September 22) will be the autumn equinox for the UK and unofficially marks the start of the new season [autumn]. After the autumnal equinox the days become shorter, and the nights become longer.

What time will the autumn equinox take place?

This year’s autumn equinox will be at 8.21pm tomorrow (September 22).

What is the other annual equinox?

There is also a vernal [spring] equinox which occurs in March each year. As you may have guessed this marks the unofficial start of spring in the Northern hemisphere with the nights becoming shorter, and the days becoming longer. In the Southern hemisphere the seasons differ.

How is an equinox different to a solstice?

Solstices mark the start of summer and start of winter but are – in a way – the opposite of equinoxes. The summer solstice is the longest day of the year; the winter solstice is the shortest day of the year; while during equinoxes the day and night are equally as long.