Re [APML]: Just 6th magniture from earth - what from space?

["Nils Olof Carlin" <nilsolof.carlin@swipnet.se>]

Len,

You may gather partts of the information from
http://www.efn.org/~mbartels/visual/nils/blackwel.html
where is my analysis of some wartime data about visual thresholds
(the data used by R Clark in Visual Astronomy of the Deeep Sky).

The data show that the visual threshold (in a statistical sense) is largely
dependent on the background brightness - dark skies on Earth (according to
Brian Skiff) are no darker than 22 magnitudes/square arcseconds (MSA - a
rather unwieldy unit - the more, the darker), and since most of the
background is scattered light by interplanetary dust (that so far
astronauts cannot get clear of I think), skies won't be much darker, but
does anybody know (in visual magnitudes) how dark sky the Hubble telescope
sees?

Against a background of 22 MSA, the threshold is somewhere around mag 7
(rising to about mag 8 for 25 MSA or darker) but assuming 0.5 mag loss
through the atmosphere, this corresponds to 6.5 mag threshold at ground
level at the darkest sites.

Dark skies,

Nils Olof


> If we can only see to a little past 6th magnitude from a really good
> dark site on earth, what would our limiting magnitude from space be?
> I was not sure what the answer was. 
> But, if I can learn that detail, I'd like to take some photos that would 
> show how an astronaut might see the stars.  I presume this is more than
> feasible.    Can anyone help with the answer?    Thanks    LenN
> 
>