What is Autumnal or Spring Equinox?

Not every day’s duration is same as every night’s duration. So, how many of us like to have a long day or a long night. Long day is good if we have a lot of works to do. After a long day, it is human nature to wish for a long night to have a sound sleep. Ya, irrespective of age, most of us love to have long days when it is a birthday or any other special occasion whether a celebration or a festival.

But a date when the duration of day and night is same.. exists. It is called Autumnal Equinox. Around the globe, in every place, the length of the day is same as the length of the night. Autumnal equinox is also referred as Vernal Equinox. Earth’s northern hemisphere’s spring is the southern hemisphere’s autumn, and vice versa. Hence, the name autumnal or vernal (spring) equinox.

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What is Autumnal Equinox or Vernal Equinox. 

Earth revolves around the sun and rotates around itself with a slight tilt in the body. Hence, it is obvious, when earth revolves around the sun, the earth faces all the directions of the sun, north, west, south, east. So, when the equator of the earth faces exactly the northern part of the sun, autumnal equinox occurs, which means the length of the duration is longer than the usual days, and autumn because the change of season occurs from this day.

Why is the length of the day and night same?

When Earth revolves around the Sun, the sun rays reflect on earth and hence forms day. Similarly, when the Earth cannot face the Sun, it remains dark and hence forms night.

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From the Earth the Sun appears to be like a disc, due to its huge mass, rather than like a point of light. As the Earth rotates around itself, the Sun also rotates not as a solid body, but it spins deferentially. That means that it rotates faster at the equator of the Sun and slower at its poles.  The Sun follows a lower and lower path through the sky each day until it is there for exactly 12 hours. This point in the Sun’s path occurs on or before two days of September 23 and is called the Autumnal Equinox.  So, the Sun rises exactly in the east and Sun sets exactly on the west. Which means the Sun is visible to the viewer form the Earth for 12 hours and invisible for the rest of the 12 hours and hence form equal day and night.

Continuing to follow a lower and lower path through the sky (with the days getting shorter and shorter), the Sun reaches a point (called the Winter Solstice, occurring on December 21/22), beyond which it can’t go any lower.

Though cannot personally experience the equal length of day and night, by anyone, can have a psychological satisfaction if you wish to rest for more as the night on this date is longer than any other date.

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