The cosmic event signifies the start of astronomical autumn…

The UAE’s Autumnal (or September) Equinox is set to fall on Monday September 23.

What is the Autumnal Equinox?

There are two equinoxes each year, one in March – the Vernal or Spring Equinox and one in autumn. Equinox translates to ‘equal night’ – because it’s the point in earth’s orbit of the sun, where there’s roughly equal day and night hours (around 12 hours each).

These equinoxes take place in the Northern and Southern hemispheres on the same date, but when the Northern Hemisphere is experiencing its spring Equinox, the Southern Hemisphere will be celebrating its autumnal one.

Why is it important for me?

The Autumnal Equinox signifies the start of astronomical autumn, a space yardstick that means the cooler weather is on the way. Of course there are regional weather patterns, such as the Asian monsoon seasons which mean that we’ve still probably got some of that high humidity on the way.

Why do the Equinoxes happen?

This is where it gets a little complicated…

It’s all to do with the earth’s axial alignment, that is – the north-south axis which currently (although it does change across a 40,000 year spectrum) sits at a 23.5º tilt – relative to the sun’s orbit.

Throughout the solar year – the sun’s focus, the subsolar point moves along the north-south axis peaking at the June Solstice, reaching its lowest point at the December Solstice.

The Equinoxes happen when the solar declination is at 0º. That means the sun is directly overhead at midday, aligned with the equator and the earth’s axis is neither pointing towards or away from the sun’s core. At these points, most of the planet will experience roughly equal daylight hours.

Is it on the same date every year?

Fun fact: The exact timing of the equinox varies slightly, though it’s almost always between September 22 and 24, a discrepancy that occurs because our calendars are unable to record the exact amount of time it takes the earth to orbit the sun (365.24 days). Which is why we also have leap years.

Images: Getty