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On Earth the Milky Way appears very ghostly when looked at with the naked eye, somewhat easier to see when NOT looking directly at it. Is it substantially easier to see by astronauts in space or is it largely the same?

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Astronauts need to have a faceplate on their helmets to look through, or a window on the shuttle or ISS, and these will absorb or reflect almost as much light as the 15% that the Earth's atmosphere scatters at sea level when it is perfectly clear. You can cut the 15% to 7% or so on Earth by going to a high mountain.

Furthermore, if the Sun or any sunlit part of the Earth are visible to the astronaut, these will dazzle the eyes and shrink the pupil to the point where the Milky Way is invisible, just as for the Apollo astronauts on the Moon.

On the other hand, the atmosphere reduces the contrast of the Milky Way by two effects: 1) scattering of starlight and reflected ground light, the same thing that makes the sky blue in the day and 2) the faint airglow that originates in the upper atmosphere from recombination of ions.

So the Milky Way won't appear much brighter to the astronaut, but it should have more contrast, especially in the outer edges.

By the way, if you think the Milky Way is ghostly and needs averted vision to see, then you haven't been to a truly dark site at the right time of night.

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It's certainly true that I haven't been to a truly dark site at the right time. I was looking at the time-lapse videos of the MW wondering about what it must be like for an astronaut. Thanks for the answer (thanks also to Wedge). – Andy I Jul 6 '11 at 15:31

It's somewhat an academic question. When can you see the stars best on Earth? When you are outside, in the dark, and away from lights. How often are astronauts in similar conditions? They spend most of their time indoors and when not indoors in brightly lit areas.

Nevertheless, in the right conditions (no nearby lights, passing through the shadow of the Earth) the Milky Way would be easier to see in orbit due to the absence of light pollution (which is an atmospheric phenomenon). However, since low orbits have a period of about 90 minutes and it takes nearly 30 minutes for the human eye to fully adjust to darkness it would be rather difficult to set up the right conditions and the period of viewing would be rather short.

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