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 2023 the autumnal equinox will occur on 23 September at 6:50am GMT (7:50am 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, 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. 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. 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. Find Out More Photos of the autumnal equinox "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 Find out more See what's on What’s On Events at Royal Museums Greenwich. Planetarium shows We Are Guardians Join Earth's fleet of state-of-the-art satellites for an immersive exploration of their role in safeguarding our planet Daily shows Adult £12 | Child £6 | Student & Under 25: £8 Royal Observatory Talks and tours Meet the Experts: Britain’s Royal Yachts Cultural icons or regal excesses? Discover the history of royal sailing craft in this free lunchtime gallery talk Wednesday 29 November | 1pm-1.30pm Free Queen's House Planetarium shows The Sky Tonight A classic guide to the night sky presented live by a Royal Observatory Greenwich astronomer Daily shows Adult £12 | Child £6 | Student & Under 25: £8 Royal Observatory Planetarium shows Starstruck Discover the birth, life and death of a star presented live by a Royal Observatory Greenwich astronomer. Weekends and holiday weekdays in November Adult £12 | Child £6 | Student & Under 25: £8 Royal Observatory Experiences Queen's House Ice Rink Relaxed Sessions Suitable for anyone who needs a calmer, more relaxed environment to get the most out of their visit 28 November, 6-6.45pm | 11 December, 6-6.45pm | 3 January, 6-6.45pm Adults £8.50 | Children £5 Queen's House Experiences | Christmas The Queen's House Ice Rink Discover the most beautiful outdoor ice skating location in London 23 November 2023 - 7 January 2024 Adult from £17 | Child from £10 Queen's House Free displays Sea creatures: real and imagined See this beautiful banner created by Willow Dene School, inspired by maps and monsters in the National Maritime Museum Open daily | 10am-5pm Free National Maritime Museum Exhibitions Our Connection to Water Life source, sacred ritual, scarce commodity? Seven artists share what water means to them at the National Maritime Museum Open daily | 10am-5pm Free National Maritime Museum Exhibitions Astronomy Photographer of the Year See the world's greatest space photography at the National Maritime Museum Open daily | 10am-5pm Adults £10 | Concessions £6.50 | Children £5 National Maritime Museum Exhibitions The Van de Veldes: Greenwich, Art and the Sea From across the sea, an art revolution is coming. Discover the art of the Van de Veldes at the Queen's House 10am-5pm daily | Closing 14 January 2024 Free Queen's House Free displays | Identity Pioneers: A Renaissance in South Asian Creativity A series of portraits of South Asian creative individuals, on display at the National Maritime Museum. Are you ready to meet the pioneers? Open daily | 10am-5pm Free National Maritime Museum Free displays Rethink Residency Learn about artworks displayed in the Rethink Space by four young resident artists, inspired by the National Maritime Museum's Our Connection to Water exhibition November 2023 – February 2024 | In line with museum opening times Free Entry National Maritime Museum Events and festivals Season of Identity Unpick the threads of Britain’s global connections and identities in a series of events at Royal Museums Greenwich October 2023 - March 2024 Free Entry In Greenwich 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 all Planetarium show ticketholders and Royal Observatory visitors Royal Observatory Talks and tours Behind the scenes tours Explore the inner workings of Royal Museums Greenwich and see conservation in action on one of our guided tours Second and fourth Thursday of every month (see page for details) | 1.30pm Adults: £16 | Members: £12 Prince Philip Maritime Collections Centre Talks and courses Teacher CPD: New approaches to teaching the history of Transatlantic enslavement With Stella Dadzie and Hannah Cusworth Thursday 30 November 3pm - 5.30pm FREE for UK school teachers and educators National Maritime Museum Talks and tours | Identity Seeing Ourselves: Sharon Walters in conversation with... Rudy Loewe Join artists Sharon Walters and Rudy Loewe for a discussion exploring representation in museum spaces CANCELLED Free Entry National Maritime Museum Family fun | Identity 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 Talks and tours BSL Tour: The Van de Veldes: Greenwich, Art and the Sea Join John Wilson for a tour of our exhibition at the Queen's House, exclusively for Deaf and hard of hearing visitors Friday 1 December | 1pm-2pm Free Entry Queen's House Talks and tours | Observatory lectures Think Space Lectures Listen to astrophysicists from across the UK talk about cutting edge research in space science See page for details Free Online Workshops | Talks & courses Saturday Art Club Join the weekly creative drop-in for young people aged 13-16 Saturdays from October - April | 10am-1pm Free National Maritime Museum Family fun Coder Dojo Be inspired by the collection and create computer programmes, animation, art and electronic experiments in response First Saturday of the month Free Prince Philip Maritime Collections Centre 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 Saturdays Free Entry National Maritime Museum Workshops | Identity 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 (+ £1.00 booking fee) Prince Philip Maritime Collections Centre