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I looked for images of a nice sunlit ISS crew cabin interior and predictably didn't have much luck. Most hits were mentions of the sunlight the astronaut would leave behind on earth, or enjoy again after returning.

But I found a few images of astronauts (possibly) enjoying some sunshine. I found one interior photo of Terry Virts with sunshine on his face, and a few exterior shots of Andre Kuipers, Paolo Nespoli and a group shot of Alexander Gerst, Reid Wiseman and Max Suraev, looking out through a cupola window with sunlit faces. Paolo Nespoli is shielding his eyes from direct sunlight, and it looks like Andre Kuipers is wearing sunglasses??

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above: TOP: Andre Kuipers, Exp. 30, BOTTOM: Paolo Nespoli, cropped/enlarged from image below.

I can imagine there are a number of reasons why the cupola windows would generally be set to block the sun, so letting sunshine into the crew area may be limited or discouraged, but I'm wondering if astronauts sometimes feel like opening the shades and letting natural light in at least once in a while.

Question: Do ISS astronauts occasionally let the sunshine in for a natural light "fix" - in other words to get a refreshing few minutes in natural lighting for a change? If so, are there limitations or restrictions associated with doing so?

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above: ISS042e016586 (11/26/2014) --- NASA astronaut Terry Virts in the International Space Station on Earth sunrise Nov. 26, 2014 looks through the cupola window while checking the "dosimeter". The cupola allows the crew 360 degree vision around the station for both photos and operating the Canada arm to pull spacecraft up to the station ports. From here.

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above: European Space Agency astronaut Andre Kuipers, Expedition 30 flight engineer, is pictured in a window of the Cupola of the International Space Station, backdropped by the blackness of space. ISS030-E-270550 (21 April 2012). From here.

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above: Paolo Nespoli in the Cupola of the International Space Station. It has seven windows and provides a pressurized observation and work area for astronauts, according to the European Space Agency. From here

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above: (From left) Expedition 40/41 crew members Alexander Gerst, Reid Wiseman and Max Suraev peer out of the cupola. From here.

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  • $\begingroup$ "Billy-bob, now throw that ol' door wide open, but don't forget the screen door, we don't wanna let a whole bunch o' bugs in. Peggy-Sue, roll back the awning on the skylight. Let's ignore the moonshine & get us some sunshine" (non southern US version) Does the ISS even have enough window space to let the sun flood in? $\endgroup$
    – Andrew Thompson
    Commented Dec 13, 2016 at 10:16
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    $\begingroup$ Define "natural light fix". If you mean a dose of Vitamin D, like we get from sunlight on Earth, then the answer is no. All astronaut exposure to sunlight has to filter out ultraviolet, which is what creates Vitamin D. As a result, ISS astronauts have to take Vitamin D supplements. $\endgroup$
    – called2voyage ♦
    Commented Dec 13, 2016 at 15:33
  • $\begingroup$ @called2voyage it's up there. Question: Do ISS astronauts occasionally let the sunshine in for a natural light "fix" - in other words to get a refreshing few minutes in natural lighting for a change? If so, are there limitations or restrictions associated with doing so? $\endgroup$
    – uhoh
    Commented Dec 13, 2016 at 16:00
  • $\begingroup$ @uhoh Define "natural lighting". Do you just mean, "Are they allowed to look out the windows, and if so what are the limitations?" or does it actually have something to do with the light itself? They are exposed to lots of light in the station. I know I'm being pedantic, but it has a meaningful difference here as I pointed out above. $\endgroup$
    – called2voyage ♦
    Commented Dec 13, 2016 at 16:03
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    $\begingroup$ @uhoh Ok, great, thanks for clarifying! So it is purely about the psychological value. $\endgroup$
    – called2voyage ♦
    Commented Dec 13, 2016 at 16:19

2 Answers 2

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I cannot find a definitive answer to this one. Obviously, they open the windows sometimes to take pictures, but from what I can tell (from most pages that I have read) they actually keep the windows closed most of the time. This is because of the effect of the variable sunlight on their circadian rhythm. For example, this was Terry Virts's explanation (Baltimore Magazine):

What about sleeping in space? Yeah, you get sunrise and sunset every hour and a half, unless you’re in high beta [orbit]. I went through a week with no sunsets.

It’s like living in Scandinavia in the summer or something? Right or Antarctica in the winter. It’s just constant sunlight. So you close the windows and you don’t know what the sun is doing and you set your alarm to GMT [Greenwich Mean Time].

Interviewer's questions in bold, as in original.

This seems to be backed up by pages on astronaut nutrition (Lunar and Planetary Institute):

Vitamin D Dilemma. Our skin uses small amounts of natural ultraviolet radiation to manufacture vitamin D, which — like calcium — is vital to maintaining healthy bones. About 10 minutes of Sun each day allows our skin to make the recommended amount of vitamin D. To work outside in the space environment, astronauts have to wear space suits which shield them from ultraviolet radiation. So because astronauts cannot produce vitamin D naturally from sun exposure, they take supplements to help with this issue.

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  • $\begingroup$ where close (or open) the window (Virts' words) means something different than it does on Earth. $\endgroup$
    – uhoh
    Commented Mar 7, 2018 at 13:35
  • $\begingroup$ @uhoh Right, basically "cover" or "uncover" the window. $\endgroup$
    – called2voyage ♦
    Commented Mar 7, 2018 at 13:36
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According to Scott Kelly's book Endurance: A Year in Space, A Lifetime of Discovery, the astronauts love to look out the windows and he's seen "thousands" of sunrises in space. And the pictures you include show astronauts experiencing sunlight. So it's clear that exposure to sunlight is more frequent than just "occasional".

But most of the windows face the earth, which will mostly shade them from the sun, and they do have shutters. So it sounds like they don't just allow the sunlight to shine in for illumination while they do other things.

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    $\begingroup$ Thanks! I edited the book title to distinguish from the book about Shackleton's Legendary Antarctic Expedition. $\endgroup$
    – uhoh
    Commented Mar 7, 2018 at 15:57

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