by NoelC » Sun Dec 30, 2007 8:41 pm
elvis1 wrote:Can some one tell me why in all the pictures I see, like the one today of EARTH, and one in SEPT. of a space walk, the whole background is black but you can not see one STAR, if it is that dark (black) out there I would think that the stars should show in these pictures. thank you.
Already answered above, but I'll elaborate a bit:
For objects in the sun (e.g., the Earth, or spacewalkers) a VERY short exposure time is required. It's just the same as if you're photographing someone outside on a sunny day - you'll have exposure times like 1/500th of a second. The stars are simply too dim to show in such exposures. By contrast, a night exposure that will show stars can actually be in multiple SECONDS, instead of a small fraction of a second.
The dynamic range of a camera just isn't wide enough to capture both the very dim stars and the sunlit subjects at the same time.
-Noel
[quote="elvis1"]Can some one tell me why in all the pictures I see, like the one today of EARTH, and one in SEPT. of a space walk, the whole background is black but you can not see one STAR, if it is that dark (black) out there I would think that the stars should show in these pictures. thank you. :)[/quote]
Already answered above, but I'll elaborate a bit:
For objects in the sun (e.g., the Earth, or spacewalkers) a VERY short exposure time is required. It's just the same as if you're photographing someone outside on a sunny day - you'll have exposure times like 1/500th of a second. The stars are simply too dim to show in such exposures. By contrast, a night exposure that will show stars can actually be in multiple SECONDS, instead of a small fraction of a second.
The dynamic range of a camera just isn't wide enough to capture both the very dim stars and the sunlit subjects at the same time.
-Noel