Quote:
Originally Posted by Stonius
Ah, that's what I needed to know. A good article - thanks for posting. The critical passage for my understanding was the following;
"In such a case, the object will always appear somewhat brighter than the background, because its own light will be added to the skyglow. But if the combined light is only a few percent brighter than the background, it will not be detectable."
So given that an ideal dark-sky site is around 22 and objects can be detected up to a maximum of 3 magnitudes fainter, does that place a limit on terrestrial visual observing for 25 mag/arcsecond^2, no matter what the size of your telescope?
So any telescope bigger than 19" makes everything brighter, but is no better at separating out low surface brightness objects from the background, since the limiting magnitude of a 19" scope is the same as the lowest possible skyglow at a dark sky site. Is that a correct extrapolation?
Cheers
Markus
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Hi Markus,
The statements made by Tony Flanders are estimations derived from his own personal experience using whatever telescopes he had at the time. And remember, we are specifically talking about surface brightness here. Even at the darkest possible site, the sky will have a minimum inherent skyglow value. Is this exactly 22 mags/sq arcsec as set by a SQM meter?
Whether the limit of 25 mags/sq arcsec for objects applies to telescopes of much larger size is an unknown here. Maybe you could get a bit more but not much more. Also, we are looking at the limits of detection of the human eye with whatever eyepiece we are using in this telescope. And, the sensitivity of one person's eyes can be very different to another persons. I'm not sure that you could give a definitive number as most objects are not evenly bright.
Regards, Rob