Bright lights solve mystery of bright nights
July 6, 2017 7:22 AM   Subscribe

The Romans referred to it as the “nocturnal sun”. Later accounts describe it as an unexplained glow – bright enough to read a book by – that would sometimes light up the night sky. Owing to present-day levels of light pollution, it's difficult to experience this phenomenon – known as a "bright night" – first hand. But two Canadian scientists believe they've unravelled the mystery behind how these bright nights occur.

They analyzed two years' worth of atmospheric data collected by the WIND imaging interferometer (WINDII). It's one of ten instruments aboard the Upper Atmosphere Research Satellite that measure chemical and physical processes in Earth's upper atmosphere. To find factors that would cause peaks in airglow and create bright nights, the researchers ruled out meteors and aurora, which have their own distinct signatures.

Solving the Centuries-old Mystery of Rare ‘Bright Nights’:

Ultraviolet radiation from the sun interacts with oxygen molecules in the atmosphere on a regular basis, occasionally splitting them into negatively charged oxygen ions. When these ions meet each other again and recombine, the reaction gives off energy in the form of visible light.

This reaction is called airglow, and it’s something that researchers have been measuring for well over a century with specialized instruments. It often appears in pictures from the International Space Station, manifesting as a thin green curve hovering above the surface of Earth. The faint gleam isn’t all that rare —the authors estimate that it’s occurring somewhere around the planet about seven percent of the time — but airglow is normally invisible to us down here on the surface, as it is too faint to see.

But on rare occasions airglow lights up the night sky due to the “stacking” of high-altitude atmospheric waves, which can multiply the intensity by a factor of 10. When the wave frequencies align, their amplitudes increase, and when up to four of them combine at a certain longitude, the night sky comes alive.
posted by mandolin conspiracy (19 comments total) 48 users marked this as a favorite
Very cool! I've read about this!
posted by Katjusa Roquette at 7:32 AM on July 6 [2 favorites]

Very cool! I've never heard of this!
posted by djeo at 7:50 AM on July 6 [5 favorites]

This reminds me of how sometimes, when camping out in the woods with the Boy Scouts, it seemed like the sky was lighter near the horizon for quite some time after sunset. This would have been in the upper Midwest.
posted by Halloween Jack at 8:00 AM on July 6

I wonder if this has anything to do with the occasional flashes of green light that appear on the horizon at sunset from time to time.
posted by infinitewindow at 8:07 AM on July 6 [1 favorite]

So it's not Yog-Sothoth parting the veils?
posted by GenjiandProust at 8:08 AM on July 6 [13 favorites]

Green flash is generally understood to be due to the refraction of sunlight rather than being generated inside the atmosphere.
posted by flabdablet at 8:10 AM on July 6 [4 favorites]

So it's not Yog-Sothoth parting the veils?

Of course it is, but the powers that be are hushing it up, using "science" like this to hide the truth while they make bargains with the hideous Old Ones.

I have it on good authority that they are close to getting what they want - to be eaten first, leaving the rest of us to suffer untold terrors in the eternal night to come.

posted by nubs at 8:13 AM on July 6 [20 favorites]

This was super interesting until the stuff about climate change made me depressed again.

"Oooooh! A cool phenomenon I've never heard of!"

"Yep! It's going to happen more often now that we've broken the Earth."

posted by Pater Aletheias at 8:37 AM on July 6 [2 favorites]

I'm pretty sure I've seen this before. My room growing up had a skylight. The area we lived in was fairly dark with minimal light pollution. I woke up one night and it was so bright, I decided to read the book that I'd been reading before an enforced lights out. My mother came up and yelled at me to turn off the lights, given the amount of light spilling out from my door. I hid the book at invited her to see that there were no lights on. I went back to reading afterwards and never saw it happen any other night.

I'd always chalked it up to an extremely bright full moon (which there was that night), but this make much more sense.
posted by Hactar at 9:11 AM on July 6 [4 favorites]

Years ago I was on a canoe trip in the BWCA and we were on an island that was either in Minnesota or Canada very far from city lights. It was remarkable how much light there would be at night, especially with the lakes on all sides reflecting the moon and stars. One night I remember it being almost daylight. I thought my eyes were getting really well adjusted or I was overtired from paddling but others mentioned it too and our guide said something like "Oh yeah that happens up here. I haven't seen it in a few years though" The next night was back to normal moonlight.

We went swimming in extremely cold but very bright (relatively) conditions at about midnight. That memory is still very vivid but I never thought to try to look up what caused it. The science is really neat and it doesn't take away from the spirituality/contentedness of that night.
posted by Clinging to the Wreckage at 9:15 AM on July 6 [5 favorites]

I thought I was experiencing this once while soloing (backpacking) in the Porcupine Mountains of Upper Michigan. I was bathing in Mirror Lake around 11pm and noticed that the sky was still blue overhead. Wow! Sike-a-delik!

Then I realized that although the Porkies enjoy all the benfits of inclusion in the Eastern Time Zone, they were geographically almost as far west as St. Louis MO (-90.19). Quoddy Head, Maine (-66.95) was in the same time zone and "eleven pm" was a social construct to which the Earth and Sun paid little heed.

Later that night I saw Ursa Major. (Well, it looked pretty major to me.) Fortunately, there was no food in my tent, and after sniffing around a bit, it gallumped on down the trail. Glad I took that bath in the lake after dinner.
In historical reports, people did not really mention what was going on in the sky, said Dr. Shepherd. “They were just aware that suddenly they could see things in their environment.”

. . . it is nearly impossible to make out a bright night when it occurs in most places, let alone find a photograph of one. When many of the observations took place, cameras weren’t yet invented. And a photograph from Earth of the bright sky at night wouldn’t be that impressive, said Dr. Shepherd. It’s something to experience firsthand.
More and more, I appreciate the existence of phenomena that cannot be fully recorded, that must be experienced directly or not at all.
posted by Herodios at 9:48 AM on July 6 [4 favorites]

So it's not Yog-Sothoth parting the veils?

That has not yet been ruled out. I think even the most pragmatic investigators would rebel, though, at a 1d6 SAN loss for just going outside at night.
posted by ricochet biscuit at 9:57 AM on July 6

So it's not Yog-Sothoth parting the veils?

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̲͙̘̟̬̠̳͇͓͕̰̕̕͡ͅH̵҉̥̙͉̝̖̺͇͙͘E̸̢̧̡̖͇͍̭̥̺̥̱̗̝̹ͅ ̀͟҉͕͈̜̗̩̺̙̪̥̠̼̱̞͚̠̬̘̟C̨̗͍͇̺̞̳͈̠̣̗͇̹͖̞̟̼͎̗̝͜Ǫ͏̵̡̜͉͇̮͉̯͚̯͉̘͈̬͉̜̣̞͓M̵̡̙̞͙̭̼̣̼̰̲̩̺̦̩ͅͅE̷̵̗͙̱̟̜̟̫͖̣̠̝͝͠S̷̨̯̬̩͎̖͍̮͙̳͚̳̤͓̰̩̺͓͓̗͜.̸̵̜̣̞̺̥̘̀ͅͅ
posted by Splunge at 10:20 AM on July 6 [3 favorites]

I've accidentally captured airglow-caused bright nights when doing landscape astrophotography.

It doesn't really look like anything other than a really bright sky, and it actually kind of ruins astrophotgraphy because it will wash out most of the stars and contrast. (Note, some of the glow in that picture along the bottom is light pollution. There isn't much light pollution at that location, though.)

I've seen it with my own eyes in variety of places, but especially in the the deep desert. There have been times I've been out in the desert and the whole sky is glowing. It's almost like the sun never fully sets and it's twilight all night long, with the airglow ramping back up right after nadir all the way until dawn.

It's really noticeable if you've also seen the same desert sky on a moonless night without as much airglow, when the sky can be an inky black between the stars and it's so dark on the ground you can barely see your own hands in the starglow.
posted by loquacious at 11:55 AM on July 6 [13 favorites]

I've also experienced something that could well have been this phenomena (down to the reading in bed with no artificial light, like Hactar). Would have been around 1988 or '89?
posted by eviemath at 2:43 PM on July 6 [1 favorite]

I was hoping that the cause was going to be the gegenschein.
posted by kiltedtaco at 8:23 PM on July 6

I was hoping that the cause was going to be the gegenschein.

How in the starry heavens am I just now hearing about this for the very first time!? Or even thinking about it? Of course this has to be a thing.

I have a new astrolandscape photograph to try to take, thank you. I might actually be able to capture this. I don't think it'll be that aesthetically/artistically interesting, but it's a technically interesting target and challenge.
posted by loquacious at 2:42 AM on July 7

The Astronomy Picture of the Day archive has some pretty cool photos of gegenschein:

The Gegenschein Over Chile

A Gegenschein Lunar Eclipse

Airglow, Gegenschein, and Milky Way
posted by mandolin conspiracy at 1:11 PM on July 7 [4 favorites]

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