Autumn equinox 2023: When is it and what does it mean?

A woman wearing black tights and boots walks through the woods, kicking up red, yellow and orange autumn leaves on the ground
The colours of leaves will change from green to red, orange and yellow as autumn gets underway. (Getty Images)

The end of summer is nigh, which means autumn has come knocking at our doors.

As we bid adieu to warm summer days and prepare for the chill of longer nights and shorter days, the equinox marks a significant time of change for Northern Europe and the US.

One of the most prominent and visual changes that will occur is that the leaves on trees will begin to change colour from green to yellow, orange and red.

According to the meteorological calendar, the first day of autumn always falls on 1 September. However, the astronomical calendar considers the beginning of autumn to be when the autumn equinox occurs.

Read more: When is the Stonehenge Autumn Equinox 2023 and how does it work? (Salisbury Journal, 2-min read)

It is also an exciting time for people who enjoy moongazing, as the Harvest Moon - the last “supermoon” of the year - will light up the sky shortly after the equinox.

A bright red full moon, known as the harvest moon, rising above Birmingham
The Harvest Moon, which will arrive shortly after the autumn equinox, is a delight for moon watchers. (Getty Images)

When is the autumn equinox?

In 2023, the autumn equinox falls on Saturday 23 September.

What is the autumn equinox?

During the equinox, the number of hours of day and night are almost equal as the sun shines directly on the equator. This means there will be roughly 12 hours of day and 12 hours of night on that day.

There are two equinoxes a year, the other being the spring equinox. The next spring equinox will occur on 20 March 2024.

Read more: When will the last supermoon of 2023 be visible in September? (Evening Standard, 2-min read)

According to the Merriam-Webster Dictionary, the word “equinox” is derived from the Latin word “aequus”, which means “equal” or “even”, and “nox”, which is the Latin word for “night”.

After 23 September, the days will become shorter and nights longer, until the winter solstice, which is the day with the shortest period of daylight. This day will take place on or around 21 December in the northern hemisphere, according to the Met Office.

A mother, wearing a yellow raincoat, and a father, wearing a blue hoodie, hold hands with their young daughter between them as they walk through a field in the evening
The autumn equinox means shorter days and longer nights are coming. (Getty Images)

There are two solstices a year. The second is the summer solstice, which occurs around 21 June and marks the day of the year with the longest period of daylight.

When is the Harvest Moon?

The Harvest Moon is the full moon of 29 September, less than a week after the autumn equinox

The fuller phases of this moon lights the fields for harvest collection, giving it its name, the BBC Sky at Night magazine explained.

A pilot boat on the sea as a full moon, known as the harvest moon, begins to rise on the horizon
The Harvest Moon may be best to see when it is low on the horizon on a clear evening. (Getty Images)

The Harvest Moon may have a red or orange hue. This is because, at this time of the year, the Sun sets almost due west, while the full moon rises near to due east.

When the moon is low on the horizon at this time, its light is filtered as it travels through the Earth’s atmosphere and red light is scattered the least, which will give the moon its bold colour.

Sighting the Harvest Moon will depend on the weather conditions, but a low and clear horizon will give you a better chance of seeing it rising.

When do the clocks go back?

In 2023, the clocks will go back on the last Sunday of October (29 October). Britons will be able to enjoy an extra hour in bed on this day.