Check out this contrail picture, which prompted an extended dialogue right here at EarthSky. Soumyadeep Mukherjee in India instructed EarthSky he was photographing a sundog within the late afternoon of July 19, 2023, when the sun was low within the west, at an altitude of 12 levels. Then, he wrote:
I seen a contrail in my body (I used to be imaging at 150mm focal size). I zoomed in (600mm) and seen the colours on the contrail.
He mentioned he couldn’t see the colours with the attention alone. However they had been noticeable with the zoom. So, he captured round 20 photographs inside a span of 30 to 40 seconds, he mentioned, utilizing a excessive shutter velocity (f/9, 1/1600s, ISO 250).
After which he selected seven from which to make the collage you see at high.
However what’s it, actually?
They’re rainbow colours, sure. However this isn’t a rainbow phenomenon. Rainbows take many varieties, however, basically, they’re curved bows, seen on the other facet of the sky from the sun.
And a few folks do seize images of true iridescent clouds. We’ve seen some at our community photo page. Iridescent clouds even have rainbow colours. You can read about iridescent clouds here. However … they’re clouds.
Soumyadeep’s picture does clearly present a contrail. And, at Les Cowley’s nice web site Atmospheric Optics, Les has images and an evidence of iridescent contrails. That’s proper, they do exist!
However we weren’t certain that’s what Soumyadeep had captured.
So we dropped a be aware to Les Cowley, and he graciously replied.
Not iridescent contrails … however stunning and weird!
Les wrote:
[You can] consider plane contrails as clouds, they’ve tiny water droplets identical to nature’s clouds. These can diffract daylight to type iridescent colours. More about them on my site here.
However I feel the colours within the image are not plane path iridescence. There may be some proof for strips of skinny cloud which are under the contrails. The contrails look like lit by a really low or setting sun. The decrease cloud droplets [the clouds below the contrails] are diffracting the light of the bright contrails to type the colours.
The explanation I help this clarification is that the colours are the place the contrails are thick a ways from the plane. Have a look at the picture on my website and you will notice the colours near the plane, the place the paths are skinny.
These areas have droplets of simply the fitting measurement shaped by air passing over the wings and fuselage.
The thick trails are from moisture condensed from the engine exhausts.
An uncommon image!
Thanks, Les. An uncommon image certainly. Thanks once more, Soumyadeep!
Backside line: They appear like iridescent contrails. However, are they? We requested the atmospheric phenomena skilled Les Cowley, who gave a unique opinion.
