The September Equinox Is On Saturday: 5 Things To Know About The First Day Of Autumn.

It is time to bid farewell to the summers in northern hemisphere and welcome the fall. For people living in southern hemisphere, replace summers by winters and fall by spring. The September equinox, also known as the autumnal equinox is on Saturday at 01:54 GMT (07:24 IST). Here are 5 things to know about this important day.

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Illustration of Celestial Equator (Image: Wikipedia)

1. The autumnal equinox is that moment when the Sun crosses the celestial equator heading southward. On this day, if you stand on equator, you’ll see the Sun rise exactly in East and set in the West. Before the Southward equinox, the Sun rises and sets more to the north, and afterwards, it rises and sets more to the south.

2. This is the second and the last time in the year when Sun will pass through the celestial equator. The first time was at the Vernal equinox in March, when Sun headed northwards after the equinox.

3. The length of day and night are same at the equinox. This year on September equinox, Sun will rise at 6:43 a.m. EDT and set at 6:53 p.m. EDT. , giving us 10 minutes of day over night. Although the sun is perfectly over the equator, we mark sunrises and sunsets at the first and last minute the tip of the disk appears. Also, because of atmospheric refraction, light is bent which makes it appear like the sun is rising or setting earlier.

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Sun’s rays fall directly over equator at an equinox. (Image: Wikipedia)

4. From hereon, nights will start getting longer and days will start getting shorter in the Northern Hemisphere while in the Southern Hemisphere, it will be vice-verse. This will continue till 21st December, the day of winter solstice, also known as the shortest day in the northern region.

5. The point where the Sun crosses the celestial equator southwards is called the first point of Libra. However, due to the precession of the equinoxes, this point is no longer in the constellation Libra, but rather in Virgo. The September equinox passed from Libra into Virgo in year −729, will pass into Leo in year 2439.

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Wikimedia Commons/CC BY 2.0

 

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