[Prev][Next][Index][Thread]
(meteorobs) Re: Visual magnitude
Hello Friends,
At 19:42 10/25/96 -0400, Lew Gramer wrote:
>
>The question of how visual limiting magnitude (the 6.0, 6.5, 7.0, etc everyone
>constantly refers to) relates to "true" sky brightness (mag/arcsec^2) is one
>I've wondered about myself - and has implications far beyond astrophotography.
>
>There's no question different people will report very different limiting
>magnitudes on the same night at the same location: differences in vision,
>low-light response, color response, and even visual training are the reason.
I feel the same Lew;
The question: "How many stars do you see within that area between those 3
(very bright) stars?", gets an answer of, let us say, "4".
But then, the next question: "But don't you see a little one, just to the
right of the two near the top?", gets you a "Yes, now that you mention it."
Most of us have tried to locate, let us say, Venus before Sunset. But no,
you can't find it; not until someone else in the group finds it and points
at it: "Yes, of course, how could I have missed it before ! "
A very young Moon ?
Almost the same situation.
>However, I'd suggest that "true sky brightness" would ALSO be dependent on the
>sampling mechanism (i.e., on the individual if it were measured by eye)! In
the
>end, the only comparison which has any meaning is between two detectors
with the
>same characteristics: two film plates with the same reciprocity failure, two
>pairs of eyes with the same response, two CCDs with the same power
>characteristics, etc. Corrections to this thinking are welcome, by the way!!
I'll join you in this quest !
>That being said, though, *IS* there a simple function which can relate an
>individual's limiting visual magnitude to the true sky brightness?
Is there ?
Saludos,
Andres