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When watching this high altitude balloon video I stumbled across a weird thing: Go to 6:08 and watch as the black sky suddenly turns to blue due to a different camera position. This is an image from about 87,000 ft (26.5 km) altitude, and despite (or because of?) no longer looking towards the Sun the entire sky suddenly turns into blue for a moment. Usually, on such nearspace videos I observed the opposite: the black sky gets a bit blue around the Sun, that's obviously due to the light scattering by the very thin atmosphere when looking towards the Sun. But I haven't seen the opposite so far, except that I've seen somewhat contradictory videos concerning the sky color at the same altitude (which includes videos by ascending rocket onboard cameras).

Why does the otherwise black sky suddenly turn blue in the footage and what does the sky really look like around 87,000 ft to the human eye (I've never been to these altitudes myself)?

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The footage turns blue because the camera adjusts its settings to the darker part. It probably raised the ISO and/or the exposure time to capture more light. This results in a brighter picture. This is also visible in the lower parts of the image. They turn very bright.

I guess the camera captures quite a good impression on how dark the upper parts of the atmosphere are. There is almost nothing left that can scatter the light and this results in very dark conditions.

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  • $\begingroup$ That is to say, to the human eye the sky would look as black as elsewhere in the video? The blue part is something only the camera was able to see when looking more down? $\endgroup$ Jul 15, 2022 at 13:37
  • $\begingroup$ @WhyOnEarth if the human looks away from both the horizon and the Sun, the sky may well look just as the camera shows: blue. Human eyes have a huge dynamic range. But when looking so that the Earth takes a significant portion of the FoV, the higher part would likely seem black: because of contraction of eye pupils, because of glare, and because of relative brightness of the different directions, similarly to how you can see "black" text when looking at a projector-generated display in a lit conference room—despite the screen actually being white. $\endgroup$
    – Ruslan
    Sep 11 at 9:38

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