A Strange Vernal Equinox

Earth at Equinox
NASA

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Equinox! Does that word have zing, or what? The media love it too: No TV weatherperson neglects to say “Days and nights are equal today” even though it’s never true.

Why Aren’t Day and Night Equal on the Equinox?

It’s false because the light rays from the Sun are bent by Earth’s atmosphere and the thick horizon air, ensuring at least 10 minutes more day than night on the equinox.  (This is why the Sun appears squashed when it sets.) They are bent in such a way that we are actually able to see the Sun before it rises and after it sets. 

And things are really screwy at the poles. Those adventurers who permanently inhabit the South Polar research station experience 24-hours of equinoctial sun. No trace of night, no sign of equality. Just the Sun fully up, going leftward along the horizon like a rolling ball.

At one time they tried growing sunflowers down there to see if they’d follow the Sun, and the poor plants rotated around and around until they strangled themselves.

So if days and nights are NOT equal …

earth-sun-equinox_full_width.png

What actually happens on the equinox?

On the day of the vernal equinox:

  • The Sun rises and sets precisely due east and west. It’s the best day to find the cardinal points of the compass. From your home, it’s the easiest day to “orient” yourself. (That word’s very meaning came about because if you could accurately find east you’d know the direction to the Orient.) Mark the location of the Sun against familiar landmarks to identify those cardinal directions.
  • It’s when daylight increases by its greatest daily amount. Or decreases, if you live in the southern hemisphere.  
  • The equinox is the only time the Sun’s path is a laser-straight line through the sky. Any other day, a time-exposure photo reveals a curved solar arc across the heavens.  
  • We use the occasion to declare the start of spring. This year it happens a half hour after midnight, EDT, on March 20. But it’s before midnight (meaning March 19) in most US and Canadian time zones. 

In fact:

Prediction: No one will complain.

 

 More: Get spring equinox dates and times for your time zone.

~ By  Bob Berman

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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Daniel, what are you talking

Daniel, what are you talking about? Vernal equinox = Sunday, March 20.

See Five Planets Align in the Morning Sky

What good is this story, which refers to a period of time from late January to mid February, today, which is March 15? Too late to be of an practical use.

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