Apr 16 1999 Philips ESP-80 |
Apr 16 1999 Philips ESP-80 |
Apr 16 1999 Philips ESP-80 |
Apr 16 1999 Philips ESP-80 |
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These photos above, taken in the latter part of the afternoon on the 16th April
1999, show a distinct halo around the Sun.
This phenomenom is caused by ice crystals in the upper atmosphere, usually in
cirrus clouds.
The sunlight is re-radiated from the crystals and appears as a halo at 22.5 deg
from the sun.
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Apr 17 2002 Olympus C3000z |
Apr 17 2002 Olympus C3000z |
Apr 17 2002 Olympus C3000z |
Apr 17 2002 Olympus C3000z |
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April seems like a good month for halos as these shots taken on the 17th April
2002 atest!
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May 01 2002 Olympus C3000z |
May 01 2002 Olympus C3000z |
May 01 2002 Olympus C3000z |
May 01 2002 Olympus C3000z |
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May seems to want to show what it can do, too. These shots above taken on the
1st May
2002 at 18:16 BST (UTC +1:00)
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parrykeyw.jpg Oct 19 2002 Olympus C3000z |
pa190814no-parryw.jpg Oct 19 2002 16:00 UTC Olympus C3000z |
pa190822_parry0w.jpg Oct 19 2002 16:06 UTC Olympus C3000z |
pa190822_parry1w.jpg Oct 19 2002 16:06 UTC Olympus C3000z |
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Thanks to an alerting phonecall from Dave Brown who was shopping in Poole, I
went outside and photographed the 22º Sun Halo and the two Sun Dogs (Parhelia) on each side of
the Sun.
I wasn't able to get both left and right hand Parhelia into frame because of
obstructions.
I took around 14 frames over the next 20 mins and then went indoors to see
what the camera had acquired. A quick flick through showed a reasonable set of
pictures,
given the difficult site, and I put them into my raw photos album to deal with
later, not having seen the hidden bonus! If I had, I'd have taken a lot more shots.
Around this time I downloaded a copy of XnView from http://www.xnview.com/ which is quite similar to ACDSee viewer but is free for private use. While examining its feature set, I just happened to have one of the two Parry Arc photos in the viewer when I tested its Gamma function for the first time. This had a bug in it such that the slider shot down to the left-hand end to set a gamma of 0.01 ! This, of course, had a disasterous effect on the preview image with only a fraction of the Sun showing and the rest black. As I brought the gamma value upwards, I noticed that there was a rare Parry Arc captured fortuitously by the camera which I hadn't previously seen! The vertical slightly expanding structure above the Sun is a Pillar and is more common. It is possible to process the photos a little harder to bring out more of the Parry Arc but the other features then start to suffer degradation. Rear-Admiral Sir William Edward Parry (1790-1855) first noted these very rare arcs during his ship's entrapment in the polar ice while trying to find the North-West Passage. Ice crystals fall downwards through the cloud and tend to adopt an alignment with the airsteam they fall through. Poorly aligned (although not necessarily randomly aligned) hexagonal ice crystals form the halo. Light rays enter a crystal side face, are refracted and leave at 60 deg to the direction of the incident ray via another side face. An excellent halo simulation program for Windows 95/98 is available from Les Cowley & Michael Schroeder and contains many different types of halos and arcs. The Parry Arcs above are explained here. Further interesting Halos and Arcs may be found on Les Cowley's Atmospheric Optics site |
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All photographs (c)GC Wood 1999.
Points arising should be addressed to
