The September equinox marks the end of summer in the northern hemisphere Matt Cardy/Getty Images

The autumn equinox, or September equinox, is being marked today by countries across the globe marking the shift in the season – ringing in autumn for the northern hemisphere and spring for the southern hemisphere.

Here are five myths and facts about the event.

Myth: Exactly equal day and night

The word "equinox" comes from Latin and means "equal night" – because all points on the Earth's surface will experience 12 hours or daylight and 12 hours of darkness. This is not entirely accurate, however.

Firstly, sunrise occurs when the top of the sun's disk rises above the eastern horizon. At that instant, the disk's centre is still below the horizon. Secondly, Earth's atmosphere refracts sunlight and as a result, an observer sees daylight before the first glimpse of the sun's disk above the horizon.

Times of sunset and sunrise vary depending on the location of an observer – longitude and latitude – so the dates when day and night are closest together in length depend on location.

Fact: Days will now get shorter

From 22 September onward, the days will get shorter until the winter solstice in December, which is technically the shortest day of the year. The winter solstice happens every year when the Sun reaches its most southerly position of -23.5 degrees.

Myth: You can balance an egg

One strange myth is that you can balance an egg on its end on the equinox. If you try hard enough – and have enough patience – you can balance an egg at any point of the year.

Fact: Different cultures celebrate the equinox

Cultures across the world celebrate the September equinox in a number of different ways and the phenomenon is linked to ancient myth and superstition. A number of harvest festivals are marked around this time, including the Mid-Autumn Festival in China.

Myth: Shadows cannot be cast at noon during the equinox

Although the sun's new angle will change someone's shadow, the circumstance to allow a person's shadow to entirely disappear are almost impossible, according to Accuweather. The sun would have to be directly above someone standing on the equator when the clock struck noon.