What is the autumnal equinox – and when does it take place?

• Following a record-breaking summer, the autumnal equinox is set to take place on Wednesday, 23 September at 1.06am (BST). But what does this mean?
• Royal Museums Greenwich says that the annual event, which takes place in September, marks the beginning of astronomical autumn for the northern hemisphere .
• Meteorological autumn, which started on 1 September, is based on weather patterns and average temperatures.
• Equinoxes occur when the Sun lights up the northern and southern hemispheres equally, with the event occurring twice a year – the autumnal equinox and the spring equinox.
• As noted by Royal Museums Greenwich: “It’s the moment at which the plane of Earth's equator passes through the centre of the Sun's disk, or the moment that the Sun passes the celestial equator. On these dates, there are approximately equal hours of daylight and darkness.”