Today marks one of only two points in the year when the day and night are nearly the exact same length.
Instead of the sun rising above or below the celestial equator (the projection of the Earth’s equator into space) it rises exactly in the east and sets exactly in the west, bathing half the world in light north to south.
The two equinoxes are in autumn and in spring, always around the 23rd of September and the 20th of March.
The actual equinox is the moment when the sun crosses the celestial equator, moving southward today at 18:20GMT, signalling the start of autumn.
The autumn equinox is still celebrated in the UK by people who follow certain traditions.
Katie Rico is a Hatha yoga teacher from Rochdale. She described how she celebrates: “We welcome the changing of the seasons by soft candlelight with gentle grounded yoga, soothing breathwork and deep meditation.
“Celebrate Mabon, release the old and welcome your inner glow for cosy, darker nights ahead.”
Mabon is one of the main celebrations that happens on the autumn equinox every year.
The festival is a part of modern pagan traditions and the Wiccan religion, and celebrates balance, gratitude and the harvest.
During Mabon, Wiccans celebrate with feasts, rituals with candles and crystals and reflection; before the start of the darker period of the year.