[AZ-Observing] Re: 3,000 images combine for Milky Way portrait
- From: Brian Skiff <bas@xxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Mon, 02 Nov 2009 17:04:22 -0700
On Mon, 2009-11-02 at 16:51 -0700, J. D MADDY wrote:
> Wouldn't the Sun block out all but the brightest stars?
There's usually at least three really bright things in the sky
at least from anywhere near Earth: Earth itself, the Moon, and
the Sun.
> The pictures from the Moon have a black background above the Lunar horizon. I
> would think the craft would have to be in the Earth's shadow to see much.
> Just a thought.
The reason for that is because it was daytime(!), so the
exposures were short. There's no scattered light, so the sky is
black, okay, but those 1/125th-second exposures really limited the
number of stars that got recorded.
More generally, the sky really isn't much darker in orbit than
from a 'true dark' site on Earth. This is because the dominant
source of sky brightness at any reasonably dark site is the
zodiacal light. So unless you get well out past Jupiter, and/or
well out of the ecliptic plane, the sky isn't going to be dramatically
better than on the ground. Yes, you'll be above the airglow and
there'll be definite improvement from having no scattered light
from the atmosphere, and no excuses about clouds, but I'm guessing
the difference would be between a fair night and a really good night
from the ground --- quite noticeable I'm sure, but not overwhelming.
\Brian
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