Equinox
Equinox
Equinox is an event
which occurs twice a year when the day and night are equal at all the places on
earth. It occurs at around 20th of March and 22nd of
September. At this time the sun is exactly above the celestial equator. At the
time of equinox, all places receive sunlight and experience dark for exactly
equal time.
The earth is
tilted at an angle of 23.50 about its axis. We think that the sun
rises exactly in the east and sets in the west but it is not true except that
for equinox. From 21st march to 21st September, the sun
is in the higher excursion relative to the celestial equator, thus the
direction of sun rise and sun set are sifted towards north. During this period,
days are longer and nights are shorter in northern hemisphere and vice versa in
southern hemisphere. Exactly opposite phenomenon happens from 23rd
September to 19th of March when the sun is in the lower excursion.
Theoretically the day
and night are exactly equal on the equinox but no place experiences exactly equal
day and night, since day is always a few minutes longer due to the atmospheric
refraction. One more reason for having longer days is that the radius of sun is
larger than earth therefore sunlight always reach in more than half of the
earth thus makes the day longer.
Equinox marks the change
of season in northern and southern hemisphere.
Credits:
Image Source- Google Images
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