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Why no stars?

  1. Apr 16, 2010 #1
    Ive noticed every time i see a picture of the ISS or astronauts working in outer space there is NEVER any visible stars?
    Why is this?
    i been told that they filter it somehow since they stars would be so bright, or is there another reason

    this has been on my mind for a long time
     
  2. jcsd
  3. Apr 16, 2010 #2

    turbo

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    Dynamic range. Simple. When you see a suited astronaut or the ISS or a module being added, they are VERY bright. To image them with proper exposure, the brightness needs to be attenuated, and stars just aren't bright enough to register. This same question has been posed about shots from Moon landings, during the film-era. The answer is still the same.
     
  4. Apr 16, 2010 #3

    russ_watters

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    You don't see stars in pictures of sunlit objects in space for the same reason you don't see stars in pictures taken with a flash at night on earth*: the stars are far too dim to show up in the pictures.

    The stars are only moderately brighter to a viewer in space than they are to a viewer on earth.

    *Caveat: Most digital cameras today have a "night portrait" mode that allows you to shoot a dim background and a flash-lit foreground object at night. It does this by taking two pictures: one short exposure with the flash, then a longer exposure one without it or by taking one long exposure picture and triggering the flash part-way through: http://photography.about.com/od/camerabasics/ss/camerapresets_5.htm
     
  5. Apr 16, 2010 #4
    oh why didnt i think of that!!!
    thank you very much
    now thats cleared up
     
  6. Apr 16, 2010 #5
    There's a non-zero probability that it means that 1) all space photos are faked and 2) the people doing the faking forgot to put in the stars.

    This is a good place to use Occam's razor. It's the dynamic range.
     
  7. Apr 16, 2010 #6
    i didnt even imply any of those
    thats just ridiculous to think that
     
  8. Apr 16, 2010 #7
    The human retina has a much wider dynamic range than both digital and film cameras, so I want to know whether astronauts standing on the sunlit side of the moon, or in the ISS can see stars when they look up and away from the sun. Or is it a bit like looking up from a large sports stadium on earth when all the powerful lights are turned on - everything around the astronaut is so bright that their eyes don't become sufficiently 'night adapted' to see any but the brightest stars and planets - Sirius and Jupiter maybe. Are there reports on this?
     
  9. Apr 17, 2010 #8

    turbo

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    That's a really good question!! I'd like to know the answer to that.
     
  10. Apr 17, 2010 #9

    russ_watters

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    I don't know if there are any reports on that, but if an astronaut is looking away from everything around them that is bright then there is nothing around them reflecting light into their eyes and their eyes would adjust to the darkness, so I see no reason why they wouldn't be able to see stars. Some adjustment happens quickly, but much of our eyes' ability to adjust to changing light conditions takes several minutes.

    When I do astrophotography from my deck, I may keep the inside of my house at normal lighting levels. I can walk outside and still see stars, but not as well as if I walk outside and stay there for 10 minutes. My sky isn't all that dark though, so the difference isn't all that pronounced.
     
  11. Apr 17, 2010 #10

    Janus

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    Of course, the difference between a room at normal lighting levels and direct sunlight is a difference between 50 lux and 32,000-130,000 lux.
     
  12. Apr 17, 2010 #11
    As long as you aren't in the direct sun light, you should be able to see stars. It seems to me like having a light shined at your back whilst you are looking at the stars.
     
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