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The Autumn Equinox usually occurs on September 22 or 23, but occasionally, it can even occur on September 21 or 24.

This is why the days are still a bit longer when the Autumn Equinox begins, and a few days after that, equal days and nights start occuring. Similar is the case with sunset, because it doesn't occur until the entire Sun completely sinks below the horizon. Though the centre of the Sun sets 12 hours after sunrise, the day begins a little before the centre of the Sun rises, because the upper edge of the Sun rises above the horizon before the centre. People living far from the Equator will experience longer days.

In some places in the Northern Hemisphere, the Sun will appear to be above the horizon when it is actually below it, because of the refraction of sunlight, according to National Weather Service. However, day and night are not precisely 12 hours each on the day of fall or spring equinox. Day and Night are not precisely 12 hours eachĪequus, meaning 'equal', and nox, meaning 'night', are the Latin words from which the word equinox has been derived. After Autumn Equinox, there will be earlier sunsets and later sunrises in the Northern Hemisphere.Ģ. Equinox is a moment when Earth's axis neither tilts away nor towards the Sun. However, it is a single moment in time, when the Sun crosses the celestial equator, which is an imaginary line in the sky above Earth's equator. Equinox is an instantaneous phenomenonĮquinox is usually thought of as a phenomenon lasting an entire day. However, on the spring and autumn equinoxes, the Sun shines almost equally on the Northern and Southern Hemispheres. Because of the Earth's axis being tilted with respect to the Sun-Earth plane, the Sun shines unevenly over the Northern and Southern Hemispheres and it is the tilt which results in seasons. The Spring or Vernal Equinox occurs in the Northern Hemisphere on March 20 or 21.Įquinoxes happen only twice a year. While it is Autumn Equinox in the Northern Hemisphere, there will be Spring Equinox in the Southern Hemisphere. According to NASA solar scientist Mitzi Adams, a kind of twilight will be prevalent at the North Pole from now until sometime in October because over the next few days after the Autumn Equinox, the Sun will go below the horizon.