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corvi
corivax
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October 2008
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corvi [userpic]
There and Back Again

Flying out was annoying. My plane ran an hour late due to engine trouble, I missed my connection, and I ended up having to fly into Pittsburgh instead of Buffalo (or even Rochester). Also, TSA goons cracked my camera's casing, and I won't be able to do any more photography for a very long time, until I can afford repairs or a new camera. Unless it's pictures of polar bears in snowstorms and the insides of stars and the like. :) Three rolls Kodak Versatility 400 free to good home, as long as you shoot something cool with them.

Flying back made up for it. Someone peremptorily traded seats with me ("Well, I thought THIS was row 44. Just go sit in my seat. No, I'm not moving.") and none of her seat-mates showed up. The meek shall inherit legroom! w00t! I had an incredible view of the East Coast strung in gleaming spiderwebs over dim misty watercolor purple predawn. The sun was up by the time I got to Seattle, but I saw a glory, the first I've seen in years.

A glory looks like this:


(I drew this image in photoshop. I don't have a photo of one, because my camera is leaking light all over my film.)

They're rainbowy halos formed by mist or clouds at the antisolar point. That is, if you draw a line from the sun, through your head, and then keep going down along the line until you reach some clouds. There must be clouds on the other side of the view from the sun, so you can basically only see them from airplanes or mountains. Obviously, the viewer's shadow is on the other side of the viewer from the sun, too. So the glory shows up as a rainbow halo around your shadow's head. In this case, you can see I was sitting at the back of the plane, because the glory is centered around my place in the plane's shadow.

An older name for the glory is 'spectre' - people used to see them climbing mountains - shadowy dark figures whose heads were crowned with rings of light.

I think glories are really neat. You can't see anyone's glory but your own, and nobody else can see yours, because even if you somehow put your head between someone else's head at the sun, their body and your shadow would block the glory.

The other really interesting thing about glories is this: we don't know how they're made yet. We know they're reflected off the water droplets at least once, because they're polarized. We know there's diffraction, like in a prism, because they're all rainbowy. We know the light is doubled back on itself, probably by single reflection. We know that the size of the glory depends on droplet size in the cloud (in fact, if you watch one from a plane, you can see it flicker and dance as the plane goes over clouds with different drop sizes). But we don't know exactly how this happens, what path the light takes bouncing around inside and between the water to backscatter so brightly.

(Mie scattering theory does accurately predict a glory. But Mie scattering theory is mathematical, not mechanistic - it tells you where the light will go to, but not how it gets there. At least, such is my limited understanding. I grok atmospheric optics middling poor.)

Little things like this, spectre and glory, the secrets between sun and shadow, the hidden songs of physics, make me very happy.


Spectre. Taken by Til Credner, used without permission.

Comments

I saw a faint glory on the flight over to England. It was kind of cool...

Wow!

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=15234&item=3840410021&rd=1

Used film cameras tend to be really inexpensive now.