Originally posted by SomeoneWatching
I still don't understand why they black out the sky. Is it just to hide all the satellites?
You do realize that the way cameras work is to expose film or a CCD chip for a certain amount of time, yes? sometimes that time is short, like a day
time picture the shutter could be 1/250 of a second. High speed cameras are taking shots much, much faster than that.
Stars, satellites and distant planets light is very faint and takes shutter speeds that are a lot longer. Whole seconds to minutes in some cases.
Light reflecting off the moon's surface or the surface of the Earth is very bright. Camera speeds are fast when taking pictures of them.
Here's a picture I took of the moon through my telescope. Shutter speed was about 1/125:
As you can see, even at a shutter speed of 1/125 seconds the sunlit side of the moon is over exposed. Notice that you are not seeing any stars in the
picture. It's because it's too quick to capture any stars.
Now take a look at this picture also taken by me:
Shutter speed was around 1/50. That's the dark side of the moon being lit up by earthshine (like how the full moon lights up our nights). Slower
speed and captured fainter light, but still no stars.
Here we go, I have stars in my picture. I took it and opened the shutter for 12 seconds. Now you can see stars. And look at the moon. It's so totally
over exposed it looks like a spot light and you can not see any of it's features:
Pictures of the Earth taken from space and pictures taken on the moon in the daylight suffer the same limits: If you want to see it, it all comes down
to shutter speed. Not air. Has nothing to do with air at all.
If satellites taking pictures of the Earth were to see stars, they would have to increase the shutter speed and that would over expose the image of
the earth. It would end up looking like a white ball of light.
Same goes for images taken on the moon: to see the stars, they would have had to open up the shutters for several seconds and that would have washed
out anything else in the picture due to the sun light reflecting off the moon's surface.