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Thread: Astronauts and the stars

  1. #1
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    Astronauts and the stars

    I'm reading the section in Bad Astronomy which talks about the Nasa conspiracy theory. I understand that stars don't show up in pictures taken on the moon because of the length of camera exposure time. However, I still have a hard time seeing why astronauts in space, such as when they were in the Shuttle, couldn't easily see the stars. (p. 160) This still confuses me. What am I missing?

  2. #2
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    Quote Originally Posted by Skybear View Post
    I'm reading the section in Bad Astronomy which talks about the Nasa conspiracy theory. I understand that stars don't show up in pictures taken on the moon because of the length of camera exposure time. However, I still have a hard time seeing why astronauts in space, such as when they were in the Shuttle, couldn't easily see the stars. (p. 160) This still confuses me. What am I missing?
    I haven't read the book, so I'm not sure what it said on page 160, but it depends on the conditions. It's not easy to see stars in sunlight and with interior lights on. It certainly is possible for astronauts in orbit to see stars sometimes, though, like when they're in Earth's shadow. They can also take pictures of stars. Here's a page on deep sky images taken from the ISS:

    http://messier.seds.org/more/m-pettit.html

    You don't see too much of that because unmanned space telescopes can do it better, and most of the "cool" pictures are going to be of the ISS, spacecraft and/or Earth.

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    Try going out at night. Stand near a street light. Your eye will adjust to that light, and you'll likely not see many (if any) stars. Go somewhere truely dark, or where that other light doesn't get to your eyes, and you'll more easily see the stars.

    So it's all about context. It's not true that the crews could never see stars; but it does depend where they are and what they are doing.

    For example, part of the navigation system was a small 'scope used to locate known stars, to provide an orientation comparison/fix. So in that case, seeing stars was a vital back-up to guiding the Apollo craft.
    I don't see any Ice Giants.

  4. #4
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    The bane of astronomers everywhere is light. Any amateur astronomer can tell you stories of being out at a dark sky site with someone who flicks on a torch or lights a cigarette - and then you wait another 10 minutes trying to get your eyes dark-adapted again. With any light source around, the pupil contracts and limits the amount of light let in (there are other chemical changes in the retina as well) which makes it difficult to see faint objects.

    The space shuttle, even in the Earth's shadow and with the cabin lights down, still had a lot of ambient light around. Despite being above the Earth's atmosphere, a shuttle is not the fantastic place to see the stars that you might imagine. In saying that, some stars were still visible when the cabin lights were down, but it is not the bejewelled expanse that some claim should be able to be seen.

  5. #5
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    Eyes adapt to ambient light levels in two ways. They alter the size of the pupil (which takes less than a second) and they produce more of the light sensitive pigment rhodopsin (which takes minutes to build up). Rhodopsin also happens to be degraded very quickly by light, so you can spend half an hour or so building up your dark adaption when you go outside to study the stars, and then have it all instantly ruined by some idiot turning on a small flashlight to read a star chart. This is why astronomers use red lights when stargazing. Red light does not destroy your dark adaption.

    What that means for astronauts in space is that unless they can manage to find a dark place and give their eyes time to adapt to the low light, stars will not be easily seen. Inside the shuttle even if they turn off the cabin lights there are various lights on the control panels that will be reflected in the windows that will affect dark adaption. Stars are not bright, and it doesn't take much to render you almost entirely unable to see any but the brightest ones.

  6. #6
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    And they're in really bright sunlight for most of the time which will shine in through the windows and light up parts of the inside, so turning off the lights might not help a lot.
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