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The Equinox Error

The Equinox Error: What you “know” is wrong

Fall officially arrives at on September 22 (the same day as our Fundraiser Cat-on-Tap), at 7:54 pm when the autumnal equinox occurs. Thinking back to science class, you may recall that “Equinox” comes from the Latin words for “equal” and “night.” On the equinoxes, vernal and autumnal, we observe a day when the hours of sunlight and darkness are equal — right?

Wrong, it turns out.

For most locations on Planet Earth, there are two days when the length of day and night are very nearly equal, but these are not the equinoxes per se. Astronomically speaking, the equinox marks a singular moment in time when the geometric center of the sun’s disk crosses over the equator. That’s why we have these precise predictions like 7:54 a.m., Mountain Daylight Time.

The day of equal light and dark is known as the equilux. It falls before the spring equinox and after the fall equinox in the northern hemisphere, exactly when being dependent on your latitude, or distance from the equator.  The explanation has to do atmospheric refraction, which causes an optical illusion, i.e., the disk of the sun appears higher than it might seem if we had no atmosphere at all.



The other thing you may have heard about the equinoxes is that with day and night in equilibrium, these two days are the only dates on the calendar when it is possible to balance an egg on end. Sorry, but this is complete hooey.  Being able to get a common chicken egg to stand at attention has a lot more to do with a large helping of patience and minute irregularities in the shell which act like tiny “legs.” Go ye to your refrigerator and start experimenting with the dozen or so subjects you may have hiding in the cold and dark, just waiting for this moment. Otherwise sane individuals have balanced eggs (On their fat ends! On their pointy ends!) on any old ordinary day of the week. As a matter of fact, the world record was set by a fellow with a lot of friends and a lot of time on his hands who engineered the precision balancing of 1,290 eggs on a day not remotely cued to either equinox.


If you are feeling blue about the passing of summer, the arrival of fall and the approach of winter, I have an astronomical consolation for you: because of Earth’s elliptical orbit, summer in the northern hemisphere is five days longer than winter. This is exactly opposite for our friends in the southern hemisphere, who have five more days of winter!  So enjoy the sunshine and the golden color of Fall in the Rockies!

Our Cubs parent and child nature exploration program will be celebrating equinox on 9/18 with crafts, hikes, and activities for children ages two through four if you know any young explorers who would like to join in on the celebration.

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Catamount Institute
740 West Caramillo St.
Colo Spgs, CO 80907
Phone: (719) 471-0910
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Website: www.catamountinstitute.org
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