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.
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.
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.
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.