(meteorobs) Setting Sun Magnitude?

[Geert Barentsen]

>Does anyone know some more modern formulae or empirical measurements to
>low altitudes to get a handle on the dimming?

Hi Malcolm and others,

Have a look at http://www.amsmeteors.org/mcleod/mcleod4.html (from 
"altitude" paragraph onwards).

-> Quote: "The correction formula is 5 log secant Z, where Z is zenith 
distance."

This formula would suggest a correction of 9 magnitudes at 1 degree, but 
what's it based on? (Looks empirical...)
I do not know of other references to magnitude altitude correction.

Cheers,
Geert