It looks like we were all wrong. I got an answer from Raymond Lee, Research Professor at the U. S. Naval Academy. His comment: - - - - - . . .Your photograph shows a rather nice circumzenithal arc (abbreviated CZA), an often spectacular ice-crystal halo. Because all halos are caused by ice crystals rather than by raindrops, the CZA should not be called a rainbow, although that is most observers' reasonable first guess. For some photographs and an optical explanation of the CZA, I highly recommend my colleague Les Cowley's Atmospheric Optics website at http://www.atoptics.co.uk/halo/cza.htm Note that the moon is far too weak a light source to contribute to a visible CZA when the sun is above the horizon. - - - - - - Following his lead, I looked at Wikipedia which has a photo that is more intense than mine:
Nice to learn something new when it's real cool . . . -yoram
Andrew Davidhazy wrote: Could very well be a rainbow produced by moonlight
Christopher Strevens wrote: Or a lunar halo
Tina Manley wrote:
Probably a sun halo
On Sat, May 5, 2012 at 3:01 AM, YGelmanPhoto < ygelmanphoto@xxxxxxxxx> wrote: Here is something puzzling.
Last week I looked up into the clouds and was startled by an arc of a
rainbow that was not concentric about the sun. In fact the sun was rather
low, in the late afternoon, and the rainbow was quite high. In the image
in my dropbox at this link ,
the location of the sun is approximately at the red X in the lower left.
The sky in the direction of the sun was cloudy but the sun was very
apparent (although not as apparent in the image). The rainbow persisted
for at least fifteen or twenty minutes, dying down gradually but not
changing position.
I tried to think of what light source could produce the rainbow as I saw
it. I tried to conceive a large structure sitting behind me, some distance
away, that might reflect sunlight so that perhaps the rainbow could be
concentric (in projection) around that. Perhaps some kind of water body,
or a highly reflective building, but I couldn't think of one and anyway I
didn't think that would do.
But later, about an hour, when I went outside to look again, I looked way
up. What I saw was a bright half moon. So here's my question: Could the
moon have been bright enough to produce the rainbow I saw in the clouds
above me? I think the relevant angles might have been somewhat
appropriate, but I didn't check. In one hour the moon moves fifteen
degrees; I should have measured the angle between the moon as I saw it and
the direction to where the rainbow was . . . but I didn't.
In full disclosure, I took the photo with a 5D Mii, with my lens set to
35mm, and the only post processing I did was to add the X for the sun and
used Genuine Fractals to reduce the size of the image to 6 x 9 inches.
Comments, please?
-yoram
-- Tina Manley, ASMP www.tinamanley.com
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