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Old Aug 24, 2007, 9:29 PM   #1
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This appeared in the sky across L.Eriboll,not far from theNW cornerof Scotland, in the evening. It's nothing to do with the camera, since wife, son & I all observed it over a period of about 10 minutes as we drove along, and it was still faintly visible across the next, parallel loch a little later.

It's not an ordinary rainbow, when the sun is directly behind the observer, and the refracting raindrops in front. The sun is way off to the right, in the north-west, and in front of us, as you can see. The second image is a resized full frame at 209mm equiv.
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Old Aug 24, 2007, 9:30 PM   #2
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Telephoto shot....
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Old Aug 24, 2007, 11:28 PM   #3
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saw one just like it the other day here
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Old Aug 25, 2007, 10:33 PM   #4
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Since posting, I've developed a theory on how this effect arises.

An ordinary rainbow marks the boundary (slightly different for each wavelength) between...

(a) rays from the sun entering raindrops, refracting at the surface once, and again on the way out of the back of the drop, never to return (dark sky at higher angles outside the bow), and...

(b) those striking the drop, refracting into it, reflecting off the back of the drop, and coming back out towards the observer after a further refraction (light sky within the bow).

However, in this case the sun is in front of the observer. But the light & dark, and the colours, are the right way round for a rainbow. So I think a patch of cloud immediately behind me may have been brightly illuminated by a shaft of the light from the sun, providing a secondary 'sun' behind me. There must have been an invisible sprinkle of rain ahead of me to provide a segment of rainbow in the usual way. If any meterologists have a better explanation, I'd like to hear it, please.

From the exif files, there was 11 min between my first & last shots of the effect, and about 1.5 miles in a straight line, 4.5 miles by road. Here is the last image of the sequence, showing the light-dark boundary well, and which my wife pointed out last night is a better silhouette anyway.

Please excuse the digression from photography. However, it is precisely all about front & back lighting, with three passes along the same light path, instead of two.

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Old Aug 25, 2007, 10:49 PM   #5
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Alan, you might want to research this phenomonem some more. I think I've read about this somewhere and there may be a name for it. However, it may be a reflection from a window or something shiny producing just a portion of a rainbow.

Most interesting.

Cal

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Old Aug 25, 2007, 11:44 PM   #6
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calr wrote:
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...it may be a reflection from a window or something shiny producing just a portion of a rainbow.
Thanks for that suggestion, Cal. Quite possibly you're right. Can't think what it was, though, because there were big empty hills behind, and it persisted over such a distance and time from many viewpoints. Sadly I've only seen it the once in 58 years.

Obviously, my pantomime-like antics with my camera, which amuse my family until boredom sets in, should in future include a bit of "LOOK BEHIND YOU".

Alan
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Old Aug 26, 2007, 12:04 AM   #7
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calr wrote:
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...might want to research this phenomonem some more...
It could be a fragment of a "Colourful supralateral and infralateral arc"...form when rays pass between the side and basal (end) faces of singly oriented hexagonal columns"

Looking at the diagram in this reference, I think the angle between sun, apparent location, and me is about right.

See...http://www.atoptics.co.uk/halo/supinf.htm, found from... http://en.wikipedia.org/wiki/Categor...ical_phenomena

Thanks for the stimulus to look it up straight away.
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Old Aug 26, 2007, 1:03 AM   #8
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Alan, nice job researching the phenomenon I've heard refered to as a SunDog. You are correct, Sunlight gets refracted through ice crystals and forms a small rainbow effect. You did a terrific job of capturing the spectacle.
Well done,
Steve
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Old Aug 26, 2007, 11:11 AM   #9
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Wikipedia is really growing into something fantastic. They have detailed information on just about anything you can think of. The information ranges from basic to highly detailed technical discussions.

I never knew there were so many different kinds of optical effects that can be observed in the sky. I've seen sundogs, halo around the sun and moon and double rainbows.

Good work, Alan.

Cal

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Old Aug 26, 2007, 11:35 AM   #10
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calr wrote:
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Wikipedia......optical effects that can be observed in the sky.
I remembered to look in Wiki for these effects because Selvin gave us a link when introducing "Sun's rays" a couple of months ago. I looked up 'Sun Pillar' then, when 'bhammitt' posted a picture of one.I'd forgotten it until you woke me up, Cal.
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