Looking up on 2010-05-15

How was this made?

A camera with a wide-angle lens was pointed at the zenith. A timer triggered the camera once every 20 seconds starting at about 13:00. The movie compresses about five and half hours into a few minutes. The image is aligned so that the compass points are arranged (approximately) as follows: West at the bottom, North to the right, East at the top, and South to the left.

The contrails that form at different times provide a great deal of information about the motion of the atmosphere. They are being formed at different elevations (sometimes you can see the shadow of a contrail being cast onto clouds below) and show the complex motion of the atmosphere.

Assuming that the jets are moving at 250 m/s gives some estimates for the speeds of various motions of approximately 20 m/s to 25 m/s.

The 22 degree halo was a remarkably persistant feature that afternoon. It's caused by hexagonal, columnar ice crystals that are oriented randomly. Presumably these crystals are high above (perhaps below?) the rest of the clouds we see as the halo doesn't seem to be affected by the other formations that we see. Toward the end of the movie we can glimpse parts of the upper tangent arc and then still later the parhelic circle as well as the halo. A single sun-dog (parhelia) is visible as well in the south sitting on the parhelic circle outside of the 22 degree halo.

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Last updated: Wednesday, 19-May-2010 13:06:33 PDT