To a Nacreon in Heaven

November 3, 2022 12:13 PM

In Norse mythology, the earthly realm of Midgard and the divine plane of Asgard are connected by a shimmering rainbow bridge -- the magnificent Bifröst. Though scholars debate whether the legend of this lustrous path was inspired by the famed aurora borealis or the star-studded arc of the Milky Way, there is perhaps another possible candidate: nacreous clouds [timelapse]. Also known as polar stratospheric clouds (PSCs), these breathtaking formations can be seen (quite rarely) in the high polar latitudes in wintertime at dusk, when a mass of super-cooled water ice forms so high up in the stratosphere that it reflects light from a sun that's well below the horizon at ground level. The result: diaphonous pearl-white sheets and iridescent streaks that light up the bleak twilight landscape with an otherworldly glow. (It's not all sunshine and stratospheric rainbows, though -- when mixed with nitric or sulfuric acid, these 10-15 mile-high clouds can contribute to ozone depletion over the polar caps [video].) Not a fan of winter weather? You may chance to see their more temperate cousin, the spectral and blue-tinged noctilucent cloud, which sometimes forms in summertime months north of 50° latitude (and north of 50 miles straight up). Or if you live near a space coast, you might see one of a menagerie of "twilight phenomenon" -- artificial light-clouds formed by multi-stage rocket plumes backlit by the sun -- including the spectacular space jellyfish. Just make sure to keep your eyes on the road...

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posted by Rhaomi (13 comments total)

Another simpler explanation is that in the northern lands these myths originate in, where the sun tends to hug the southern horizon, you get a shitload of rainbows all the time and they often seem to connect earth and sky.
posted by lefty lucky cat at 12:27 PM on November 3, 2022 [6 favorites]

Post title is *chef's kiss*
posted by Wretch729 at 12:43 PM on November 3, 2022 [21 favorites]

"keep your eyes on the road"
Did someone say cloud streets near Svalbard?
posted by BobTheScientist at 1:10 PM on November 3, 2022 [4 favorites]

If you like this sort of thing, lots can be found at the Atmospheric Optics website, the original version of which I first found via this 20 year old(!) post.
posted by TedW at 1:15 PM on November 3, 2022 [4 favorites]

My nomination for Bifröst is the circumzenithal arc; most people are not aware of it but it is actually pretty common. If you see sundogs when the sun is low in the sky, look straight up and you may well see a small but bright rainbow pointing towards the sun.
posted by TedW at 1:27 PM on November 3, 2022 [3 favorites]

I used to see sun dogs and moon dogs and the northern lights fairly often. Strange to think how long it's been! But I've never seen a nacreous cloud - I guess there's always going to be something about this beautiful world to experience for the first time.
posted by Lawn Beaver at 1:48 PM on November 3, 2022 [2 favorites]

Nacreous clouds at the Cloud Appreciation Society's cloud library.
posted by biogeo at 3:02 PM on November 3, 2022 [3 favorites]

Thanks so much Rhaomi. This post exceeds even my wildest expectations!

I saw a nacreous cloud just once many years ago. I had no idea what it was and it was utterly captivating.
posted by roolya_boolya at 4:10 PM on November 3, 2022 [2 favorites]

These eerie, glowing clouds keep appearing more often: The rise of noctilucent clouds may be yet another unforeseen consequence of burning fossil fuels.

What has increased in recent decades is rocket launches. As they pierce the heavens, rockets leave a wake of exhaust gases, particles, and water. “It is clear that rocket launches can perturb and create cloud layers that are noctilucent cloud layers,” Russell said.

As for the moisture, that may be coming from methane, a gas with surging emissions due to human activities like agriculture, land degradation, and natural gas extraction. When methane climbs to high altitudes, it undergoes oxidation, where it reacts with oxygen catalyzed by sunlight and breaks apart, yielding water as one of its products.

“For every methane molecule that reaches that altitude, you get two water molecules,” Russell said. “So methane is a key source of water. And if methane is increasing in the atmosphere, you can count on water vapor increasing in the atmosphere.”

posted by MrVisible at 4:37 PM on November 3, 2022

A+++ post title; surely, you have earned a place in the afterlife!
posted by GenjiandProust at 6:24 PM on November 3, 2022 [2 favorites]

back on the midgard,[*] just hanging out...
-Asperitas Clouds
-roll cloud over Lake Michigan
-Crepuscular Rays in the Atmospheric Optics of Sunlight
-at the IceCube Neutrino telescope at the the Amundsen–Scott South Pole Station
posted by kliuless at 1:59 AM on November 4, 2022

Everything about this is new to me, I so appreciate the OP and our sponsor. Thank you both so much!
posted by Bella Donna at 2:25 AM on November 4, 2022 [1 favorite]

Wow kliuless, that Asperitas Clouds story is great!
posted by roolya_boolya at 11:25 AM on November 4, 2022