The autumnal equinox occurs in September each year, and in the northern hemisphere the date marks the end of summer and beginning of autumn.

The Earth is tilted on its axis. This means that the Sun illuminates the northern or southern hemisphere more depending on where the Earth is along its orbit.

However, at two points in the year the Sun will illuminate the northern and southern hemispheres equally. These are known as the equinoxes.

When is the autumnal equinox in 2024?

In 2024 the autumnal equinox will occur on 22 September at 12.44pm GMT (1.44pm BST).

Find out more about equinoxes and solstices

Image

When is autumn?

There are three main different ways of defining autumn: astronomical, meteorological and phenological.

Astronomical

Astronomically, the four seasons centre around the equinoxes and solstices. However, there is disagreement between those who see the equinox or solstice as the start of the season, and those who hold that it represents the middle of the season.

Meteorological

By contrast, meteorologists tend to divide seasons into periods of three whole months based on average monthly temperatures, with summer as the warmest and winter as the coldest. On this basis, for most of the northern hemisphere the autumn months are usually September, October, and November.

Phenological

The third way of defining autumn is to use what are known as phenological indicators. These cover a range of ecological and biological signs, such as the leaves falling off the trees and the migration of birds to warmer climates. These events of course are greatly influenced by weather and climate, and so changing climate could cause autumn to start earlier or later than the standard astronomical or meteorological definitions.

Visit the Royal Observatory to find out more about the history of measuring time and the seasons.

Autumnal equinox facts and customs

The Harvest Moon is the name given to the full moon that occurs nearest to the autumnal equinox. Historically the light of the Harvest Moon was said to enable farmers to work late into the night, helping them to bring in the crops from the fields. The Harvest Moon usually falls in September.

Saturn also has equinoxes, but because it takes almost 30 years to orbit the Sun, they only happen about every 15 years.

Saturn Equinox
Saturn Equinox, NASA

For those located at high northern hemisphere latitudes, the autumnal equinox paves the way for increased chances to see the aurora borealis. According to NASA, the equinoxes are prime time for the Northern Lights, and geomagnetic activities are more likely to take place in the spring and autumn than in the summer or winter.

Green aurorae arcing over snowy mountains beside a still lake
Glow of Vestrahorn by Ewa Jermakowicz – Astronomy Photographer of the Year 2022 Aurorae shortlist

Mabon is a modern Pagan ritual marking the autumnal equinox. The ritual gives thanks for a plentiful harvest and recognises the need to share the Earth’s fruits in the coming winter months. It is the second of the three Pagan harvest festivals, which include Lammas/Lughnasadh and Samhain.

In Japanese culture, the autumn equinox is celebrated with the tradition of Higan. It is a time to remember deceased relatives, as well as mark the passing of the seasons. Higan officially lasts for seven days, beginning three days prior to the equinox and ending three days after it.

Because of time zone differences, the equinox can be on different days for different locations.

Reynolds' Series of Astronomical Diagrams - The Theory of Seasons
Explaining the seasons
AST0051.1 • Prints & Drawings
This diagram shows the Earth's annual rotation around the Sun, surrounded by the signs of the zodiac and the positions of the equinoxes and solstices. It is one of a series of educational cards first issued in 1846.

Photos of the autumnal equinox

Image of Glastonbury Tor's shadow with moon double the size in the background

"In 2021 I really got into imaging the Moon at a distance with something in the foreground," explains Astronomy Photographer of the Year entrant Hannah Rochford. "In this case, it is people enjoying the Full September Harvest Moon as it rises behind Glastonbury Tor.

"The first time I planned a moonrise (using PhotoPills) and saw the Moon rising was absolutely magical. I cannot explain how it felt. The perspective never fails to excite me. I took this from a few miles away from the Tor to get that ‘gigantic’ Moon look.

"Capturing the Moon is what led me into my deep-sky astrophotography journey, which is my favourite thing. A lot of people think that this is a composite, but it is one image. I took it with my 10-year-old, second-hand Canon camera."

Visit Astronomy Photographer of the Year to see more of the world's greatest space photography.

Visit the Royal Observatory

Visit the home of Greenwich Mean Time and stand on the world-famous Prime Meridian Line

What’s On

Events at Royal Museums Greenwich.

Astronomy Photographer of the Year
Exhibitions

Astronomy Photographer of the Year

See the world's greatest space photography at the National Maritime Museum
Open daily | 10am-5pm
Free
National Maritime Museum
Earth From Space
Exhibitions

Earth From Space

See the world through a satellite’s lens, and explore our changing planet at the Royal Observatory Greenwich
Open daily | 10am-5pm
Free for Planetarium show ticketholders and Royal Observatory visitors
Royal Observatory
Women of the RNLI
Exhibitions

Women of the RNLI

Celebrate 200 years of saving lives at sea at the National Maritime Museum
2 March – 1 December 2024
Free
National Maritime Museum
SENsory Social Club
Family fun

SENsory Social Club

Join the weekly online club for adults and young people with SEND
Friday during term time | 11am (Online session) or 1pm (Onsite session)
Pay what you can
Prince Philip Maritime Collections Centre
The Sky Tonight
Planetarium shows

The Sky Tonight

A classic guide to the night sky presented live by a Royal Observatory Greenwich astronomer
Daily except Thursdays
Adult £12 | Child £6 | Student & Under 25: £8
Royal Observatory
Meet the Neighbours
Planetarium shows

Meet the Neighbours

Tour the Solar System and beyond in style with this live, immersive show packed full of spectacular sights and fun facts
Weekends and school holidays in October
Adult £12 | Child £6 | Student & Under 25: £8
Royal Observatory
Coder Dojo
Workshops

Coder Dojo

Be inspired by the collection and create computer programmes, animation, art and electronic experiments in response
First Saturday of the month (unless stated otherwise below)
Free
Prince Philip Maritime Collections Centre
Make, Do and Maintain
Workshops

Make, Do and Maintain

Join our community of makers at The Prince Philip Maritime Collections Centre
First Saturday of every month | 10:30am-12:00pm
Free (+£1 booking fee)
Prince Philip Maritime Collections Centre
Character Encounters
Talks and tours

Character Encounters

Visit the National Maritime Museum every Saturday to discover a different character from history with their own fascinating story to tell
Every Saturday
Free
National Maritime Museum
Cutty Sark Rig Climb
Experiences

Cutty Sark Rig Climb

Experience life at sea and climb the rigging of one of London's true icons
Weekends 10am-5pm | Closing 31 October
Adult: £55 | Child (10-17): £45 | Under 25/Student: £49
Cutty Sark
Ted's Space Adventure
Planetarium shows

Ted's Space Adventure

Join Ted the bear on an adventure around the Solar System in this special live planetarium show for under-7s - perfect for little astronauts everywhere!
Weekends and school holidays
Adults £12 | Child £6 | Student & Under 25: £8
Royal Observatory
Observatory Unlocked
Experiences

Observatory Unlocked

Drop by and chat with our Royal Observatory Explainers as they bring science and astronomy to life
Saturdays and Sundays
Included with Royal Observatory admission
Royal Observatory
Meet the characters of Cutty Sark
Family fun

Meet the characters of Cutty Sark

Meet colourful characters from Cutty Sark’s past and hear astonishing stories about life at sea in the age of sail
Weekends and Fri-Mon in school holidays
Included with entry to Cutty Sark
Cutty Sark
Audio Universe: Tour of the Solar System
Planetarium shows

Audio Universe: Tour of the Solar System

Experience the Solar System like never before - by travelling on a spacecraft that can turn the objects in space into sound!
Weekends and school holidays
Adult £12 | Child £6 | Student & Under 25: £8
Royal Observatory
Sea shanty singers
Family fun

Sea shanty singers

Join our resident sea shanty groups at Cutty Sark on the first weekend of every month as they sing traditional maritime songs
First weekend of every month
Included with entry to Cutty Sark: £20 Adult | £10 Child
Cutty Sark
Saturday Super Store Tours
Talks and tours

Saturday Super Store Tours

Come behind the scenes and explore the stores at the Prince Philip Maritime Collections Centre
Saturdays at 1.30pm
£12
Prince Philip Maritime Collections Centre
Discover Sundays
Family fun

Discover Sundays

Each Sunday come and explore the Museum's collection through hands on creative activities
Term time Sundays | 11am - 1pm | 2pm - 4pm
Free | Drop-in
National Maritime Museum
Black History Month talks at the Queen's House
Talks and tours | Black History Month

Black History Month talks at the Queen's House

A special programme of tours and workshops celebrating Black History Month
Sunday 6 October 2024 | 10.45am - 4pm
Free
Queen's House
Play Tuesdays
Family fun

Play Tuesdays

Bring your under 5 on a different adventure every week! Explore the Museum together through song, dance and stories
Term time Tuesdays | 10.30am, 11.30am, 1.00pm, 2.00pm
£4 per child and accompanying adult | Under 6 months free
National Maritime Museum
Shipkeeping in action
Talks and tours

Shipkeeping in action

This is your chance to meet the team who care for and conserve Cutty Sark
Monthly | See page for details
Free for Cutty Sark ticket holders
Cutty Sark
Lunchtime Concerts
Events and festivals

Lunchtime Concerts

Enjoy musical performances in the Queen's House given by students from Trinity Laban Conservatoire of Music and Dance 
Select weekdays (see page for details) | 1pm-2pm
Free, drop in
Queen's House
Wonders in the Deep
Talks and tours | Member events

Wonders in the Deep

Hear stories from the world-famous underwater archaeologist, Mensun Bound.
Thursday 10 October 2024 | 6.30pm-7.30pm
Free for Members | £8 for non-Member tickets SOLD OUT
Cutty Sark
Delve Deeper: Specialist tours
Talks and tours | Museum Lates

Delve Deeper: Specialist tours

Delve deeper into Royal Museums Greenwich's collection on our specialist tours of the Prince Philip Maritime Collections Centre for over 18s.
Monthly | 7-8.30pm
£20 Adults
Prince Philip Maritime Collections Centre
Saturday Art Club
Workshops

Saturday Art Club

Join the weekly creative drop-in for young people aged 13-16 during term time at the National Maritime Museum
Saturdays from October 2024 - April 2025 | 10am-1pm
Free
National Maritime Museum