It is generally accepted, I understand, that under optimal conditions, magnitude 6 is the faintest visible to the unaided Human eye.
What about in space? What would the faintest magnitude be if you were looking into deep space, while in space, and NOT having some such object as the sun or a planet in your field of vision?
Magnitude Visibility
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Topic authorDollan
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Magnitude Visibility
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Spaceman Spiff
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Of the top of my head, I think the one 'airmass' worth of atmosphere right above you takes off 1 magnitude. However, I'm not sure, but stellar magnitudes must be published after correcting for this. Thus, it may not be the case that you'll see star's of mag. 7 in space, but rather that we usually only see stars of mag. 5 as mag. 6 here on Earth... Er, am I making sense? 
Spiff.
Spiff.
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Spaceman Spiff
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Sorry Dollan, I think I was garbling myself up there. I had to look into it. I found something in the Aug 2000 Newsletter of the Alburquerque Astronomical Society: http://www.taas.org/times/nl/aug00nl.html.
Look for the "Ask the Experts" part by Kevin McKeown.
This chap explains that in space you would see stars down to mag 7.1, but if you could find the best place on Earth to observe, he says you could actually see stars at mag 6.8 up at the zenith.
Yes, I've heard too that mag 6.0 is the general limit. So, that fits in with 'typical' atmospheric extinction being about 1 mag which I was sure I had heard of before.
What I got muddled was thinking that if you had an atmospheric extinction of 1 mag, then mag 5 stars of would be extinguished to appear as mag 6 stars just at the limit of visibility. That's not the case, you do (just about) see actual mag 6 stars. Take away the atmospheric extinction of 1 mag, and you'd see the mag 7 stars.
Spiff.
Look for the "Ask the Experts" part by Kevin McKeown.
This chap explains that in space you would see stars down to mag 7.1, but if you could find the best place on Earth to observe, he says you could actually see stars at mag 6.8 up at the zenith.
Yes, I've heard too that mag 6.0 is the general limit. So, that fits in with 'typical' atmospheric extinction being about 1 mag which I was sure I had heard of before.
What I got muddled was thinking that if you had an atmospheric extinction of 1 mag, then mag 5 stars of would be extinguished to appear as mag 6 stars just at the limit of visibility. That's not the case, you do (just about) see actual mag 6 stars. Take away the atmospheric extinction of 1 mag, and you'd see the mag 7 stars.
Spiff.