Naked-Eye Visual Magnitude Limit

Chris L Peterson wrote:

I would say rather that scintillation and bad seeing are different but related
phenomena. In my location, they are rather well correlated (in the sense that
the stellar FWHM of both short (.1 sec) and long (1 min) exposures increases
with scintillation about 75% of the time. I occasionally have bad seeing without scintillation. I virtually never have good seeing with scintillation.

Chris,

It's easy to measure seeing, but is there a way to measure
scintillation? I agree that there is some correlation between strong
scintillation and poor seeing through the telescope, but it hasn't
been strong in my experience.

I have seen very good seeing with scintillation quite often at Arizona
sites. Just last month, I was at the future site of the 4m Discovery
Channel Telescope. We were using ~1000x on a friend's optically
excellent 10-inch to split Gamma Virginis (0.6" separation). At the
same time the stars were twinkling an average amount (there's that
lack of measurement again!). I found the same thing during a 12-night
observing trip to an observatory site in Chile that routinely
experiences seeing of 1" FWHM. There was no less scintillation than
I was used to seeing on nights in the deserts in Arizona.

When I have tried to detect the faintest star through the eyepiece of
a telescope, it is certainly affected by seeing. I think it's as much
of a reason for seeing the faint star "25% of the time" or whatever as
physiology of vision. I can't say I have tried to estimate naked-eye
limiting magnitude on a number of nights under different degrees of
scintillation.

Tom