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Sundog [Leeds UK, 10 Sep 2002 4.04pm; Fuji FinePix 2200 digicam]

We've been looking for one of these for a while. Sundogs aren't particularly rare, but as many people have a built-in aversion to looking near the sun, they're easy to miss. They don't always last long, either.

However, on 10 September 2002 Lee was out with a camera and happened to spot this. Our first sundog!

A sundog -- technically a parhelion, pl. parhelia -- is a 'ghost' sun, about 22 degrees to the side of the real sun. You can get them on both sides simultaneously, but this picture just shows one (the rainbow-coloured spot above the house). It's a halo phenomena, caused by reflection and refraction in aligned ice crystals in the upper atmosphere. They're often associated with cirrus clouds, as here, and can sometimes be just the brightest part of a complete ring around the sun (a halo).

They are also very beautiful.

To find a sundog, hold your hand outspread at arm's length with your thumb covering the sun; the sundog/s will be where your little finger is, at the same height as the sun (about 20°) ... and always remember to take great care when looking at the sun, especially through optical equipment of any kind.

We haven't yet managed to seen a full halo display, or a circumzenithal arc -- a small rainbow vertically overhead when the sun is about 20 degrees above the horizon. We'll keep looking. [30 Sep 2002: Success!]

For further information, explanations and photographs, visit the splendid Atmospheric Optics web site. See also the extraordinary book Color and Light in Nature by Lynch and Livingstone (second edition; Cambridge University Press 2001, £19.95).

Image details

Photographer: Lee
Original image: Leeds UK, 2002:09:10 16:04:25 * 1280x960 JPEG * 310 Kbytes
Camera: FUJIFILM FinePix2200
f11.00 * Exposure: 0.0013sec * ISO speed 100 * Focal length: 5.80mm
Flash: Not fired * Program: Normal * Metering: Multi-segment
Photodesk processing: gentle contrast enhancement using gamma curves

© 2002 Lee Montgomerie / Chris Terran
All images are copyright and may not be reproduced without permission

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