My bloggin' buddy Ken Spencer and I both love to watch the country slide past our windows while flying. We're both amazed more people don't watch - on our trip last week to the Midwest, most even had their shades down! Besides illustrations of fluid dynamics, shown in the last post, it was a classroom in other effects, even though it was cloudy for most of the trip.
"subsun", documented in another travel post about this time last year. Les Cowley, who runs the "Optics Picture of the Day", a great website of atmospheric phenomenon, even devoted a page to the image last Summer! While evidently pretty common, subsuns appear low with the sun high in the sky, so are likely normally unobserved. This trip, about an hour before our arrival in Chicago, likely somewhere near Kansas City if we kept to our normal route, I spotted one, this time without "subsun-dogs". It appeared as a very good, though dimmed, image of the sun without much scatter to blur the suns reflection from aligned flat ice crystals. From my first image to the last, 6 frames were obtained in 90 seconds - the extent of the subsun data collection this trip.
The clouds were dense and constant from central New Mexico to our arrival in O'Hare, and as we banked for final approach, were still above the cloud deck. I hoped-for and watched, but didn't see the Willis Tower (second-tallest building in the country) poking above the clouds. We usually have a fine view of the skyline during that final turn.
This time, however, we had an even more interesting view. Now headed west towards O'Hare, and us on the right side of the plane, we were treated to seeing our shadow. If you had been looking, you would have seen a shadow of the plane, yes, but something extra - circular bands - a glory! The photo at left was taken with the camera at full zoom of 85mm focal length, with minimal adjustments of brightness, contrast, and a slight boost of color saturation. I'll let you go to Les Cowley's page about glories to learn more rather than me wave my arms here to explain. Make sure you look at the several pages of illustrations and explanations and other examples. Now what is really cool is that you can infer the water drop size from the diameter of the glory! The subtended diameter is inversely proportional to the droplet diameter. For grins, I took the full-frame image at left, and cranked the color saturation, and made some measurements, shown at right. The sensor size is 24mm long, and the number I've carried in my head from college is that 1 degree for any lens is .01744 X the focal length, in this case, 1.48mm. Knowing the scale, the red rim of the first ring is 6.5 degrees. With Les' equation from one of those pages, the droplet size works out to 19 microns - pretty cool!
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