Daily Latitude of Equinox
Isn't there always a latitude that is experiencing equal
daylight and darkness?
Equal daylight and equal darkness means 12 hrs day and 12 hrs night.
For this study, let's assume that the Earth stands still and the Sun rotates
about the Earth.
The Sun then rotates about the earth daily, but it swings between the
Tropic of Cancer
At 23 degrees 26 minutes, 22 seconds North of the Equator and marks the
farthest North the Sun travels.
the Tropic of Capricorn
at 23 degrees 26 minutes, 22 seconds South of the Equator and marks the
farthest South the Sun travels.
Equinoxes are the days the Sun crosses the Equator. Solstices are the days
the Sun reaches the Tropic lines and turn back to the other hemisphere.
near March 21 of each year (the Spring equinox) as the Sun moves North of
Near September 21 of each year (the Fall equinox) as the Sun moves South of
Winter Solstice is near December 21 when the Sun is over the Tropic of
Summer Solstice is near June 21 when the Sun is directly over the Tropic of
Days on which Daylight and Nighttime are equal happen twice per year.
When the Sun moves above or below the equator, different proportions of the
Northern and Southern hemispheres are illuminated so the times for Day and
Night become unequal. There are times in Summer when North Pole experiences
24 Hrs of Daylight, and times in Winter when North Pole is in total darkness
for 24 Hrs.
When the Sun is directly over the equator, both Northern and Southern
hemispheres are equally illuminated and Daylight time equals Nighttime. So
it would be fair to say that the times Day equals Night is when the Sun is
over the equator.
So there are two days of the year when the night time equals the daylight
time but in the Northern Hemisphere one of those days occur just before the
Spring Equinox and just after the Fall Equinox. The opposite happens in the
Southern Hemisphere. The number of days before and after the equinoxes
depend on the Latitude.
Click here to return to the Astronomy Archives
Update: June 2012