In a recent thread about naked-eye visual star splitting, David
Knisely and Chris Peterson discussed visual magnitude limit for
unaided vision. It really does vary quite a bit between individuals.
Here's are excerpts from a posting I made on this subject to another
list in 1999.


"...We used the equilateral triangle of stars formed by eta, beta, and
mu Pegasi to guide our way to the the test stars.

....Very near my limit were HIP 113005 and 113063, both listed as
magnitude 7.4. I could hold these stars with averted vision most of
the time. I hit the wall at HIP 113092, which lies 10' west of a
slightly brighter star. It has a Hipparcos V magnitude of 7.7.

....While I stared at the screen, I had [Bernie Sanden] describe the
positions of these stars. He was able to see HIP 114833 and 114832,
magnitudes 8.4 and 8.3, respectively. Then he went on to mention HIP
113481 and 113486, which are 8.0- and 8.5-magnitude stars."

These observations were made at a dark site in southeast Arizona. I
can't say that I have ever tried to assess the effect of scintillation
on naked-eye magnitude limit, but I bet the effect is negligible.
This site at which we saw so deep is known for both bad seeing and
scintillation (which are two different phenomena).

Tom