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I'm assuming during an EVA when an astronaut is facing the station reflected sunlight reduces an astronaut's dark adapted vision to the point they can no longer see the stars until either the station enters the Earth's shadow or they turn their back on the structure. Based on reports from Apollo astronauts.
If the same holds true for astronauts in a Soyuez or a space shuttle approaching the station, how close do they have to be that they no longer see the stars?

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    $\begingroup$ There is a very large object exposed to the Sun nearby, the Earth. If they have the day side of Earth in view, their eyes could not adapt to dark. $\endgroup$
    – Uwe
    Oct 11, 2019 at 18:54
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    $\begingroup$ Quite, I think its still an interesting notion. Perhaps there's an alternate way to express the question such as "at what magnitude will an object spoil one's dark adapted vision" $\endgroup$
    – Puffin
    Oct 11, 2019 at 21:37
  • $\begingroup$ @Puffin Good point about a better way to express the question, but wouldn't that be a biology SE question? $\endgroup$
    – Bob516
    Oct 12, 2019 at 0:56
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    $\begingroup$ @Bob516 Yes, you're right. If one was going to try to evaluate an answer to the question from the bottom up then it would have two parts, one being the biology bit and the other (perhaps the bit you are after) being how to calculate the magnitude of nearby objects $\endgroup$
    – Puffin
    Oct 12, 2019 at 19:20

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Answer: Yes and no. It depends on ambient light levels and how they affect the astronaut’s dark adaptation.

On dayside transit, sunlight on ISS structure and Earthlight would produce photopic (light-adapted) illumination levels so starlight would fall below retinal sensitivity. If the astronaut could turn to exclude Sun, Earth and ISS from their field of view, their eyes could dark adapt and see stars. But NASA isn’t paying them the big bucks to stare out the window in class.

A Google Image scan produced no stars in dayside ISS photos. This one is typical:

enter image description here

Nightside EVAs occur since the longest ISS EVA was over 8 hours (4 orbital periods). Nightside transit has much lower ambient light levels, but the astronauts need significant artificial light to perform their duties:

enter image description here

If astronauts’ dark adaptation is not messed up by artificial lighting on the night side, they should get a spectacular view of the heavens. Here is a photo of Comet NEOWISE (maximum magnitude 1.0) 2 days after perihelion

enter image description here

Earth taken from the International Space Station, on July 5, 2020. (NASA via AP)

There was a full moon on the night this photo was taken, so the Earth below is illuminated by moonlight.

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