From Icy Iridescence To Starry Incandescence

The edge of a patch of cloud is fringed with pink and blue-green iridescence this past weekend shortly after sunrise. Photo: Bob King

While walking the dog on a recent morning, I noticed a pack of cirrocumulus clouds in the sun’s direction glowing with hot pinks and blue-greens. It was one of the most vivid displays ever of the phenomenon called iridescence.

Tiny, uniform-sized water droplets or ice crystals in certain types of clouds bend or scatter incoming sunlight in all directions. Scattered light waves pass through one another just like the waves from two stones dropped in a pond. Where the waves’ crests coincide, that particular color or wavelength of light is reinforced and appears bright; where troughs coincide, the waves cancel or interfere with one another and that color is weakened or missing.

A corona or series of small, colored rings around the moon is another form of iridescence or light scattering. A single, large ring or halo forms when light is refracted through ice crystals. Photo: Bob King

Since light is composed of every color of the rainbow and each color is bent by a different amount, a series of vivid, alternating hues results.

Iridescent clouds are more common than you think, but we usually don’t notice them because they’re most colorful when near the sun, and we normally don’t look in that direction. The key is to watch  for feather-edged cloud paddies shot with delicate ripples that look like parallel waves. If you see one near the sun, block the sun with you hand or hide it behind a building and scan its edges for color.

There’s something about the purity and intensity of iridescent colors that provokes a visceral reaction – if you’re a human that is. I looked down at my dog that night and her attention was focused – as always – on the ground below.

A batch of brilliant blue stars burns its way through the lovely Lupus 3 dark cloud located about 600 light years from Earth. The photo was taken the ESO’s MPG/ESO 2.2-meter (86.6-inch) telescope at the La Silla Observatory in Chile. Click to enlarge. Credit: ESO/F. Comeron

Light is always up to something. The European Southern Observatory (ESO) posted a wonderful new photo of a stellar nursery in Lupus 3, a dark cloud of cosmic dust in the constellation Lupus the Wolf. Like the Orion Nebula, dust and gases are collapsing into new stars in the dark core of the cloud. Not that we can see them. Visible light doesn’t penetrate light years of dust very well, but telescopes designed to see into the infrared part of the spectrum can detect the heat radiating from these starry babies.

In stark contrast to the dark nebula’s closely-held stellar secrets, a clutch of young blue stars blazes forth on the other side of Lupus 3. These were also once invisible too, but as they grew, the stars heated up and developed strong stellar winds that blasted through the dusty clouds to their present-day blaze of glory. In a future century, the same transformation from darkness to light will happen all over the cloud.

This wide-field view shows the dark cloud where new stars are forming along with cluster of brilliant stars that have already burst out of their dusty stellar nursery. Click to enlarge. Credit: ESO/Digitized Sky Survey 2

The glowing blue aureole around the brightest stars isn’t a camera effect. That’s light at work again. Remaining dust left in the open hole created by the newborns scatters their intensely bright light much like the way fine particles in cigarette smoke glow in sunlight.

If you’ve ever wondered how the sun (and planets) got here, look no further than Lupus 3. Cocooned away in some dark interstellar cloud, the sun grew by gravitational collapse nearly 4.5 billion years ago. It almost certainly had siblings, too, but trying to find them is like tracking down your ancestors from 45 million years ago. The sun’s soulmates have long since scattered across the local spiral arm of the Milky Way. Still, that doesn’t stop astronomers from proposing how it might be done. Click HERE for an interesting article on the topic.

10 Responses

  1. H.Bob

    AstroBob. I love these deep space photographs. So clear and so amazing to see. We are a lucky generation of humans to be able to see such images of our universe. As for your dog, he was probably too busy contemplating the multiverse or string theory to distract himself with mere iridescence! Maybe he can make a blog appearance one day!!

    1. astrobob

      H. Bob,
      I totally agree. We are a fortunate generation indeed. If only my dog could talk, I’d learn so much from her, including, no doubt, string theory!

      1. H.Bob

        (You may have already seen this, but…) if you ever have the chance to see Hubble 3D IMAX at an IMAX screen, it is a fantastic digital experience of travelling through the universe. It’s an educational film and plays at the Science Museum in London, but must be playing all over the USA too.

  2. Interesting, I know so little about the atmosphere – kinda wish I had taken a class on it back in college. I did see a strange bright cloud the other day. I was wondering if you’d take a look:

    Not sure if it is iridescence or just a small rainbow through the backlit jet stream. What do you think?

    Thanks, Eric

    1. astrobob

      Hi Eric,
      I really like your astrophotography experiments using your iPhone. Some of them are very nice. Way to push it to the limit. It looks like iridescence to me in your photo, but what’s striking is the cloud formation. It’s so singularly thin. Could it possibly be part of a jet contrail?

  3. Giorgio Rizzarelli

    Awesome Moon corona photo, Bob.. I did one a couple of nights ago with 2 rings and thought it was the top..and now I see you did one with 4! How did you succeed? Just luck or local climate, or possibly helps going in darker/cleaner skies? (I was in city). Thanx!

    1. astrobob

      I shot that multiple-ringed corona two years ago. It was to date the most exceptional one I’ve ever seen.

Comments are closed.