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I came across this image taken on the "Balcony" at over 27,000 ft (8,200 m) elevation, beneath the summit of Mount Everest. So many stars can be seen on it even though the Sun has risen. Do Everest climbers really see stars after sunrise or is the image a long-exposure one or something?

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  • $\begingroup$ The more I look the more I'm certain that's a composite image. The shadows don't point away from the sun, and I don't think the fisheye lens is enough to explain that (looking at the most central shadows especially. And the host page is an advertising company after all. It's linked from a page about an image capture/augmented reality project, which certainly means some processing and implies some combination of images $\endgroup$
    – Chris H
    Commented Nov 10, 2021 at 13:23
  • $\begingroup$ Related video. The last scene matches some of this image, but with a tighter crop and a different camera angle, though the preview if you hover over the progress bar looks like a closer match (the preview appears to be of a 3d version that I can't enable here) $\endgroup$
    – Chris H
    Commented Nov 10, 2021 at 13:31
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    $\begingroup$ @ChrisH Oh it's just snow. blush $\endgroup$
    – Giovanni
    Commented Nov 10, 2021 at 14:06
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    $\begingroup$ @ChrisH One can reportedly see Venus in daytime, if you know where to look and have eagle eyes. But I meant seeing stars easily, with likelihood of spotting one randomly without searching the sky. Just like after sunset or before sunrise. $\endgroup$
    – Giovanni
    Commented Nov 10, 2021 at 15:19
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    $\begingroup$ I've certainly seen Venus with the sun low in the sky, but haven't looked in broad daylight $\endgroup$
    – Chris H
    Commented Nov 10, 2021 at 17:00

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The reason that you can't see stars in the daytime is that the atmosphere scatters sunlight and effectively blots them out. But even where I live, a dark sky area, the brightest stars are visible during twilight. Not just the planets, Sirius for example becomes visible before the sky is dark.

With the sun on or near the horizon, the effect of scattering is reduced.

At high altitudes the atmosphere is much thinner. The scattering is therefore similarly reduced and yes, you can sometimes see the brightest stars in daytime. This would not necessarily be the case every day and at all hours of the day.

Although I haven't been to Everest myself, friends who have report that some stars can be seen on clear days. I haven't interrogated them as to whether it was near sunrise or sunset.

(But your picture does look like a composite)

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  • $\begingroup$ My picture actually shows snow as ChrisH found out. Why do you consider Wiltshire a dark sky area? The highest point of the UK is the Ben Nevis at just over 4,400 ft. The daytime sky becomes considerably darker above ~25,000 ft I guess. When in an airliner at cruise altitude the sky above me is much darker up there, but I think I've never seen stars out of a plane during day. Once I have seen a star at twilight out of a plane, when the Sun might still have been above the horizon, but it's a long time so I don't remember exactly. I've seen possible stars on a picture of a view out of Concorde. $\endgroup$
    – Giovanni
    Commented Nov 10, 2021 at 16:14
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    $\begingroup$ From nightblight.cpre.org.uk/maps there are some pretty dark region of Wiltshire (e.g. much of Salisbury Plain). But when looking low in the sky that's a bit misleading as I found the other riding round the edge of the Cotswolds Gloucestershire when the Northern Lights came much further S than normal: I was in the 2nd darkest band, maybe even the darkest, but the light pollution from Gloucester, Stroud etc. was scattered by a few low clouds. Car lights didn't help either. Even straight up, I couldn't see as many stars as in the Scottish Highlands, but far more than in a city $\endgroup$
    – Chris H
    Commented Nov 10, 2021 at 16:46
  • $\begingroup$ So you're talking about light pollution, but during day we can't see stars because of the brightness of the closest hydrogen-burning star, the Sun, and therefore the lit blue atmosphere. $\endgroup$
    – Giovanni
    Commented Nov 10, 2021 at 17:43
  • $\begingroup$ @Giovanni that's the only way I can interpret "dark sky area", but this still helps when the sun is low $\endgroup$
    – Chris H
    Commented Nov 11, 2021 at 9:30

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