Strange, Night-shining Clouds Light Up The Summer Sky

A splendid display of noctilucent clouds spreads across the northern sky in this wide-angle picture taken at 10:45 p.m. last night. The streak at top is an airplane contrail. Details: 35mm lens at f/3.2, ISO 400 and 6-second exposure. Photo: Bob King

I don’t know why I get so excited about noctilucent clouds. Normally I’m cursing out the clouds because they come at the most inopportune times, blocking some rare celestial treat from view. Not last night. On the way to dark country skies, I noticed a wisp of white in the northern sky in mid-twilight around 10:15 p.m. By 10:30, the twilight had deepened enough to reveal a low bank of noodly blue clouds. Ah-hah! The noctilucent clouds were back.

Check out the undulations and stripes in this bank of NLCs due north last night about 10-15 degrees high. The bottom noctilucents are reddened by absorption from denser air lower in the atmosphere. Photo: Bob King

Night-shining or noctilucent clouds (NLCs) are visible on and off at higher latitudes during the early summer months. They’re not common by any stretch. In the past 30 years of sky watching I’ve seen only a half dozen displays.

Cirrus clouds, the ones that look like feathers wafting across the daytime sky, are typically about 10 miles high. Composed of ice crystals, they float near the top of the lowest, thickest layer of air called the troposphere. Noctilucent clouds share the realm of the Greek gods, basking in sunlight well into the night at an altitude of some 50 miles. That’s nearly as high as the aurora borealis, which can shimmy down to a tickly 60 miles.

The blue color of NLCs is very obvious in thisi photo taken with a telephoto lens. The star is Capella in Auriga. Photo: Bob King

NLCs are creatures of the Earth’s mesosphere, a rarefied blanket of air extending from 30 to 53 miles high. Most meteors burn up in this layer. It’s also extremely cold up there – temperatures at the top drop to 130 below F. Like lower clouds, the night-shining variety are composed of ice crystals, either condensed directly from the thin air or seeded by tiny dust particles. Likely sources for the dust include meteor debris, volcanic dust and even water exhaust from the era of the space shuttle.

This photo was made two hours after sunset when the NLCs were an electric blue above the last bit of twilight arch. As you can see, the stars were out by this time. The clouds are also visible 1.5 - 2 hours before sunrise. Photo: Bob King

Because of their great height, noctilucent clouds reflect sunlight long after sunset when other clouds have gone grey and colorless. That’s why they’re called “night-shining” in the first place. Their color is imparted by the ozone layer located 12-19 miles overhead. The reds and oranges of reflected sunlight are absorbed by ozone on their way down to our eyes, tinting the clouds blue. Pretty cool.

We see noctilucent clouds well after sunset when other clouds have gone dark because they're much higher up and can still catch sunlight and reflect it back to Earth. Credit: NASA

Between 10:30 and 11 o’clock last night the NLCs grew brighter and more detailed. Stripes, undulations, curls and streaks were all plainly visible to the naked eye.  Last night’s was the best show I’ve ever seen. Still, I wished I would have carried binoculars along to better appreciate the subtle folds and ripples the photos picked up so clearly. Next time, next time.

Between 10:45 and 11 ( 1.5-2 hours after sunset) the clouds slowly began to fade from top to bottom, but this was also when they were most striking. In a dark sky, they glowed an eerie plasma blue as if powered by electricity. By 11:15 the sun was too far below the horizon to provide the light to sustain them. What was once an amazing display disappeared with the coming of night.

Once the sky was truly dark, clouds of another sort tracked across the eastern sky. These were made of stars - the Milky Way. Photo: Bob King

The clouds are best viewed from the northern tier of the U.S., Canada and the northern half of Europe, though they’re occasionally sighted at lower latitudes.  Displays usually start in June and wrap up by early August.

To find them, go out during twilight at hour or more after sunset and look low in the northern sky. Regular clouds appear dark grey at that time, but NLCs will grow brighter against the darkening sky. They also don’t move as fast or change shape as quickly as lower clouds due to their high altitude. Think of airplanes. Close by, they move quickly, but higher up, they take more time to cross the sky.

I’ll be out the next clear night on cloud watch and hope you will too. To learn more about NLCs and how you can contribute your observations to help improve our understanding of them, check out the Noctilucent Cloud Observers’ Homepage.

11 Responses

  1. Roma

    Wow great shots Bob… and as always, super informative. I loved the sky last night— I should take a photography class on how to take photos at night. In theory, I know how… but I can’t quite figure it out. If you ever teach a class on photographing the night sky, let me know and I’ll drive up to Duluth!

    1. astrobob

      Thank you Roma! I do occasionally teach night sky photo classes here. I’ll let you know when I do so again.

  2. Marie

    PS I grew up on near the shores of Lake Superior and cannot recall seeing the Milky Way. I am vexed!
    Memories of the aurora borealis are, however, vivid.

  3. Mike Thiele

    Good morning Bob! Great photos as always! Would you please provide the info for the Milky Way photo? Time taken, camera and lens, exposure, time exposed, etc. Thanks!
    Very good article. I have seen these clouds too.

    Now through the night there is a glow to the north as the earth revolves and the sun tracks east to dawn.

    Take care. Summer is good. Always seems to disappear fast. Hope your wife is healing well.

    Mike

  4. valina

    Hi Bob,

    I dropped in on your site last week because I knew we’d be on an airplane to Europe on June 12. What amazing luck I had!! My face was glued to the window for about 6 hours of our flight, watching all the celestial artwork over the clouds after take-off from Texas. About the time we were flying over Main and Nova Scotia, I noticed a glowing above the twighlight. About 10 minutes later, I saw the same display you picture here, only from 33000 feet in the air! I have pictures, but no way of loading them up until I’m back in Texas. I think I’m the only one in my family who was all excited. Even my dad, who sailed for years in the Dutch navy did not know what “noctilucent” clouds were. It’s not often I get to show him something new. Thanks for the info, and I’m sooooo glad you saw them too. My sighting is confirmed!

  5. Chris

    Last night as i was driving home, at 00:10, I noticed something was different about the sky. In the distance were some white clouds that were visible. They weren’t thin and wispy like yours in the photo though, they were quite tall and full. I checked Google sky maps on my phone (I live in the UK) and the moon and sun were about the same position a bit below the horizon. Could these have been the same clouds as you mentioned our are there another type of clouds that are visible at night?

    1. astrobob

      Hi Chris,
      It’s possible. The clouds aren’t always wispy. They can form thicker blankets and be higher in the sky at higher latitudes like yours in the UK. In the northern U.S. (47-49 degrees north) they’re quite low and generally wispy or “pleated” but very rarely thick and high up.

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