Olympus-OM
[Top] [All Lists]

Re: [OM] Name that phenomenon

Subject: Re: [OM] Name that phenomenon
From: Skip Williams <skipwilliams@xxxxxxxxx>
Date: Wed, 10 Nov 1999 20:08:42 -0500
Joel,

Through personal experience and my consultation of several sources, including my bible on the effects: "Rainbows, Halos, and Glories" by Greenler (1980). I believe that you've photographed one of two phenomena, either a portion of a sun pillar or a parry arc/tangential arc/circumscribed halo, all of the latter tangential to the "normal" 22 degree halo.

1. I really think it's a portion of a sun pillar. They are usually formed by internal reflection of sunlight through flat plate ice crystals oriented edge-on. (Pencil-shaped crystals can also produce pillars, but they're usually more equal above/below the sun when visible and not as strong as flat plate pillars.) Sun pillars are seen only near sunset and can last for many minutes, with the sun both above and below the horizon. They are usually strongest near and AFTER sunset, as the flat crystals need less of a tilt angle to reflect/refract the light back to us. The reason you saw only a spot instead of a vertical pillar is that the cloud with the correct ice crystals was only a thin cloud, instead of broad enough to show the whole pillar. Ken Norton's explanation is partially right, in that the light is being reflected and refracted to your line of sight. But the reflection/refraction is taking place WITHIN the flat, hexagonal ice crystals floating in the cloud.

2. As Christoph Hertzler pointed out, it could also be a portion of a upper tangential arc or parry arc or circumscribed halo to the standard 22 degree halo. The only thing that would lead me away from that cause is that such arcs typically are not so spot-concentrated as a sun pillar segment. Also, the clouds would have to relatively uniform vertically above the sun for the arc to remain visible as the sun descended, as the arcs's line of sight is fixed just outside the 22 degree angle from the sun. They also don't stay around very long with the sun gets below the horizon. I think this effect is unlikely in your photo's case.

Also, it is not the common "sundog" or 22 Degree Parhelia. These occur _only_ just outside the 22 degree halo and at the same altitude as the sun. The only phenomenon spot-concentrated above the sun would be an intersection of the 22 degree halo and an upper tangential arc, which is not as strong as a sundog.

If you're interested further, Robert Greenler's book is great with diagrams, color photos, and has quite a bibliography for more reading. Try Amazon.com or Sky Publishing.

Hope this helps.  Pillars are neat.  I don't see them often where I live.

Skip


At 11/10/99 10:30 AM  -0600, you wrote:
At 06:32 AM 11/10/1999 -0700, you wrote:
>At 10:55 PM 11/9/99 -0600, Joel Wilcox wrote:
>>Oly Shooters,
>>
>>I wonder if there is a name for this phenomenon:
>>
>>      http://members.tripod.com/jdubikins/test/test.html
>>
>>It will look a little like the sun at about 10 degrees above the horizon,
>>but it is actually a reflection off the clouds that was quite concentrated
>>and lasted for nearly 10 minutes after sunset was complete.
>
>
>Joel:
>
>This is a variation on an optical meteorological phenomenon called
"subsun."  In this case, I'd be tempted to call it "supersun," since it's
obviously happening above the sun, rather than below it.  Everything else
is the same, however.
>
>Garth

Thanks Garth.  These "above" and "below" perspectives are obviously
anthropocentric.  Should I assume because of the name that it is usually
seen at high noon or some such?  It looks a little like a sundog, without
the prism effect.

Joel Wilcox
Iowa City, Iowa USA

< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >


-----------------------------------------------
Skip Williams
Westfield, NJ
skipwilliams@xxxxxxxxx
-----------------------------------------------


< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >


<Prev in Thread] Current Thread [Next in Thread>
Sponsored by Tako
Impressum | Datenschutz