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Re: interesting pic for a classroom exercise?



I saw this once watching a football game on TV. It was evening in San
Francisco and the bored TV crews turned one of the cameras to view the
Moon and zoomed way in so that the Moon appeared large. Just as they cut
to this camera, a jetliner flew through the field of view leaving a
beautiful turbulent wake.

While I haven't done anything quantitively with this, I'm pretty sure
this is an example of the flow visualization technique called "optical
shadowgraphy." Very well collimated light is bent by variations in the
index of refraction of the fluid to produce the observed patterns. It is
not that the wake is "opaque" in the sense of absorbing the light, but
rather the light has been deviated so that it misses the telescope.

Tim Sullivan
sullivan@kenyon.edu

"Kilmer, Skip" wrote:

By a lucky coincidence, last week, just after I bought a solar filter for my
little Meade scope, I saw the same thing. No more than a couple of seconds
after I found the sun, a 737 flew in front of it. One of thowe WOW
experiences. My question for the group, however, is why the exhaust trails
are so opaque. They were in what I saw, just as in this photo. I looked at
the plane a few seconds later, and the it was not leaving visible contrails.
Refraction phenomenon, maybe?
Skip