Why is it when we look up into the night sky we can see stars. but when you see pictures taken from the ISS you don't see any stars. Why is this?
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1$\begingroup$ Related: absence of stars in Moon photographs $\endgroup$– Nick TFeb 18, 2014 at 23:16
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4 Answers
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The reason is that the exposure on the camera is set so that the main subject of the image is properly exposed, ie not too dim and not too bright. Because the typical objects being photographed are quite bright, the image detector (camera) will not get enough light from the stars for them to show up.
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2$\begingroup$ Or with other words: For pretty much the same reasons, because of which we cannot see stars from earth at noon. $\endgroup$ Feb 18, 2014 at 18:11
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$\begingroup$ @Wrzlprmft: Even after our discussion, that gives me a headache — maybe someone else can shed a bit light on the matter: in space, take two pictures with different exposure times and one will show stars and the other won't … on earth, take two pictures with the same exposure time, the night-picture will show stars, the day picture won't. I think the crucial difference is, that in space, you change the detector, while the day-night difference is mainly due to a change in the signal that arrives at your detector. $\endgroup$– ValryneFeb 18, 2014 at 20:34
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There are plenty of pictures from the ISS in which you can see stars.
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3$\begingroup$ Note that these photos with Earth and stars will always be on the night side $\endgroup$– Nick TFeb 18, 2014 at 23:16
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It's because of the short Dynamic range of the camera. The human eye has a very large dynamic range which allows it to see at the same time, lights of low exposure and lights of high exposure. The same problem exists when you try to capture a photo against the sun light. Either the sky is completely white and the object is correclty lightened, or the sky is correcly lightened and all the objects are dark unlike what you see with your eyes...
There is a topic in photography called High Dynamic Range (HDR) which consists of taking pictures of different exposure levels, and assembling them by computer (sometimes by the camera itself) in order to approach what we can see with the human eye.
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This is for the same reason that you don't see any stars on moonwalk pictures or videos; the reflected sunlight from Earth (or in my example, the moon) is so much brighter that it washes out the faint starlight.
