The Old, Misunderstood Equinox

Autumnal Equinox Facts

Autumnal Equinox

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The autumnal equinox occurs on Friday afternoon, the 22nd, at 4:02 P.M.  The reason for the equinox—and the Earth’s seasons—is frequently misunderstood. 

Are Days and Nights Truly Equal?

At the equinox, the Earth will angle perfectly sideways to the Sun. Neither pole will tip toward or away from it. And therefore, as the media never tire of reminding us, days and nights should theoretically be equal.

But this is never true. Our atmosphere bends the Sun’s image upward so much that it rises two or three minutes earlier and sets that much later than it would on an airless world, and those extra five minutes of daily undeserved sunshine push the true date of equality to the middle of the following week.

And even then it’s not strictly accurate to say day and NIGHT are equal, because of twilight. If useful daylight ends about an hour after sunset, and you add in the dawn twilight too, then most places don’t have equal day and night until around November 10.  So we get more actual night than daylight for just three months, from then until mid-February.

Sets East and West

But never mind the equality business. A more precise equinox event is that next weekend the Sun rises and sets exactly in the east and west, not southeast or northwest or anything else. It’s a time of precision, and an opportunity to correctly position your sundial, that task you keep putting off. 

The Sun’s Path

Another equinox phenomenon is that the Sun then moves in a laser-straight line across the sky. A time exposure shows this nicely. By comparison, for the past six months the Sun’s path has displayed an upward curve, concave to the north, like a giant smile. Starting on Saturday, its track across the sky bends like a rainbow, with the concave part aimed downward.

Equinox Folklore

As for eggs balancing Saturday but at no other time, that’s just silly. Why should the laws of gravity be repealed just because the Sun illuminates both poles equally that day? Still, it’s fun to consider, especially if it sparks conversation about the reasons for the seasons.

If you take the equinox so seriously that you have an equinox-obsessive personality, which psychologists call EOP, you’ll contemplate the idea of equality at 4:02 PM Friday. That’s when our beloved Sun pauses momentarily, balanced and motionless, before lunging headlong toward the northern winter.

See the Autumnal Equinox page for more facts and folklore.

About This Blog

Welcome to “This Week’s Amazing Sky,” the Almanac’s blog on stargazing and astronomy. Wondering which bright objects you’re seeing in the night sky? Want to learn about a breathtaking sight coming up? Bob Berman, longtime and famous astronomer for The Old Farmer’s Almanac, will help bring alive the wonders of our universe. From the beautiful stars and planets to magical auroras and eclipses, we’ll cover everything under the Sun (and Moon)!

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