LITTLE ROCK, Ark. – Thursday, Sept. 22 was the official first day of fall and the autumnal equinox. The autumnal equinox is when most people think we have 12 hours of daylight and 12 hours of dark, but that is not the case.
Even though equinox is Latin for “equal nights,” we actually had 12 hours and 8 minutes of daylight on Thursday.
The equilux, which is Latin for “equal light” is when the daylight is exactly 12 hours long. In Arkansas, this occurs Monday, Sept. 26.
In the northern hemisphere, the fall equilux is always several days after the fall equinox. It ranges from Sept. 24 near the Arctic Circle, to Sept. 28 along the Mexico border.
Why is this?
This is because the equilux is 100% dependent on there being 12 hours of daylight. Daylight begins as soon as part of the sun rises above the horizon and it ends as soon as the entire sun sets below the horizon. This causes there to be more than 12 hours of daylight on the equinox.
This is true even at the equator. According to TimeAndDate.com, locations like Quito, Ecuador, that are on the equator have about 12 hours and 8 minutes of daylight all year long! This means locations on the equator never have an equilux.
Here in Arkansas, we also had 12 hours and 8 minutes of daylight on the equinox, but because we are losing about 2 minutes of daylight each day, we reach our equilux just 4 days after the equinox.
This varies with latitude because locations further north lose daylight at a much faster rate, so they have their equilux closer to the equinox.
The days are getting shorter each day and the next time Arkansas will see 12 hours of daylight is Mar. 16.
– Meteorologist Alex Libby
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