Circum Zenith Arc

Hi Peter, tthis is avery cool shot - congratulations on getting it published.

Great image. I love the colors. Can you tell us something about this unique formation? I'm guessing it was taken in the fall near sunset and the sun was to the upper right of this ring.

Cheers

I don't recognize the shot. This is great, whatever this phenomenon is it is certainly beautiful. Congrats on getting it published!

Tom,

sure I want to tell something about this arc.

As the name sais it's near the zenith. The zenith is the point directly above your head. Well it's not there, but if you'd make a full circle it would go around it.

It's formed by tiny ice cristals. hexagonals if I'm not mistaken, but you can find that on http://www.sundog.clara.co.uk/halo/
These cristals are normally high in the sky. So if you see a haze high in the sky or cirrus clouds there is a chance of halo activity. The most common halos are sundogs and 22 degree halo.

The most active seasons for halos differ around the world. The only thing you have to have are these cristals. In the netherlands you can see halos all year around. It's also not true that the sun has to be low above the horizon, but it is true that they occur more often if it is. I've seen a full 22 degree halo just after midday in full summer, so the sun was very high at that moment. It was magical. This shot on the other hand was taken in the late afternoon. These arcs can indeed only form when the sun is below a certain angle. I forgot the exact number, but the sun must be at least 45 degrees below this arc.

Look at this shot. This arc is the upper one. You can also see two sun dogs left and right of my hand, and the upper part of the 22 degree halo: http://www.astro.uu.nl/~hartog/nature/e ... _dog_g.jpg

Cheers

Peter