Autumnal equinox, September 23, 2015


You can only get this shot on two days each year.

I was sad to discover most of my U.S. history students (juniors) didn’t know what an equinox is. So the autumnal equinox always offers a teaching moment that ticks off the teacher raters.

Summer 2015 ended at 4:15 a.m., September 23.

This is what an equinox looks like, from 2013 photos.

From Astronomy Picture of the Day: Earth at Equinox. From the Russian meteorological satellite Elektro-L

From Astronomy Picture of the Day: Earth at Equinox. From the Russian meteorological satellite Elektro-L

Explanation from NASA:

Equinox Earth
Image Credit: Roscosmos / NTSOMZ / zelenyikot.livejournal.com
Courtesy: Igor Tirsky, Vitaliy Egorov Explanation: From a geostationary orbit 36,000 kilometers above the equator, Russian meteorological satellite Elektro-L takes high-resolution images our fair planet every 30 minutes. But only twice a year, during an Equinox, can it capture an image like this one, showing an entire hemisphere bathed in sunlight. At an Equinox, the Earth’s axis of rotation is not tilted toward or away from the Sun, so the solar illumination can extend to both the planet’s poles. Of course, this Elektro-L picture was recorded on September 22nd [2013], at the northern hemisphere’s autumnal equinox. For a moment on that date, the Sun was behind the geostationary satellite and a telltale glint of reflected sunlight is seen crossing the equator, at the location on the planet with satellite and sun directly overhead (5MB animated gif).

Wait. Animated .gif?  Cool!

The Earth at equinox, 2013; from Russan space program, via NASA.

The Earth at equinox, 2013; from Russan space program, via NASA.

The autumnal equinox is at 8:22 GMT or 4:22 am EDT on Wednesday. The two satellite images below from the European Meteosat show the sun angle on Earth from June 22 near the summer solstice and then today at the same time.  Notice the sun angle has changed dramatically, and the High Arctic is no longer seeing 24 hour daylight.

June 22 2015 from Meteosat.

Below is today at the same time.

Seviri Sep22

More:

Yes, this is mostly an encore post. Fighting ignorance requires patience.

Yes, this is partly an encore post. Fighting ignorance requires patience.

One Response to Autumnal equinox, September 23, 2015

  1. When I lived in Indiana and taught geography (which was a required subject back then), my students learned about equinoxes. Alas, geography is no longer required (is it taught anywhere?). Do students learn about equinoxes in Earth Science classes? I’m a veritable dinosaur, I guess, because I never even heard of Earth Science being taught as a course until recently.

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