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Today I saw a circle of light outside my plane window on the clouds, as if someone was shining a bright, tightly focused flashlight, or perhaps like the halo that sometimes appears around the sun. I think it was approximately where I would expect our shadow to be (at least the sun was shining on the opposite side of the plane).

A still from the video

I took a video with my phone. I move the camera around a bit to show that it doesn't seem to be an artifact of the window.

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  • $\begingroup$ Hi Crummy, I added a still from the video, as some users don't like going off site. If my edit is approved, it should appear shortly on your post, but if you have a still with greater contrast, then maybe replace my screenshot. Where were you sitting in the plane? $\endgroup$ – user140606 Jan 21 '17 at 17:45
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    $\begingroup$ Thanks, I should have done that myself. I was sitting in seat 3A on a KLM CityHopper. $\endgroup$ – Crummy Jan 21 '17 at 17:46
  • $\begingroup$ Well, you got your answer PDQ. :) I saw St. Elmos fire on an aircraft windshield at night, it's kinda creepy, crawling around, even when you know what it is. I think you come second in the pic stakes though, the one below is terrific. $\endgroup$ – user140606 Jan 21 '17 at 17:50
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    $\begingroup$ Related (perhaps even identical): physics.stackexchange.com/q/256636/17609 $\endgroup$ – Keep these mind Jan 21 '17 at 17:51
  • $\begingroup$ @Keep that's a good question, but I don't think this one is a duplicate. $\endgroup$ – Emilio Pisanty Jan 21 '17 at 18:00
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What you're seeing is called a glory, an optical phenomenon related to rainbows, caused by reflections and refraction inside the water drops in the cloud (plus some additional physics, which are not fully agreed on; cf. this question). If the cloud had been closer you would have been able to see the shadow of the plane embedded in the glory:

Image source

For more information see the page on glories at Atmospheric Optics, particularly regarding their formation. (Also, just go to Atmospheric Optics and have a browse! they've got all sorts of gorgeous stuff there.)

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    $\begingroup$ As, I think, the centre of the glory pinpoints the photographers location in the plane, I am hoping to see this in some episode of Sherlock/Elementary/whatever. $\endgroup$ – Keep these mind Jan 21 '17 at 19:08
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It is an optical phenomenon called a "glory" caused by a diffraction in very small water drops. In fact, the radius of the glory depends on the size of the drops of water and can change in a dynamic fashion as you fly above different clouds with different size of drops. It is quite different than a rainbow though.

Professor Lewin gave a fantastic lecture at MIT about the rainbow and other optical phenomenon, where he mentions glories: https://www.youtube.com/watch?v=pj0wXRLXai8&list=PLyQSN7X0ro2314mKyUiOILaOC2hk6Pc3j&index=32.

However, as pointed out in the comments, he does not provide a thorough explanation of the glory which is extremely difficult, there is still no complete explanation that is agreed upon. Still the lecture as a whole is very instructive and is worth watching.

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    $\begingroup$ The glory starts at 35 mins into the video, however its explanation does not seem to go beyond 'diffraction'. Full stop. $\endgroup$ – Keep these mind Jan 21 '17 at 18:15
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    $\begingroup$ Can you elaborate on the reasons why you think glories have 'nothing to do with reflection and refraction'? Atmospheric Optics, which is generally quite reliable, points in that direction, as does Wikipedia, but I may well be missing a better resource. And, if you do have more recent references, it may be a good idea to post it on this linked question. $\endgroup$ – Emilio Pisanty Jan 21 '17 at 18:57
  • $\begingroup$ I edited my post since that phrasing was not justified $\endgroup$ – The Question Jan 21 '17 at 20:16

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