"robert" wrote in message
oups.com...
I have a Q for someone here.
What is the formula for derriving flux (as a measure of light per unit
area per unit time) from the astronomy magnitude scale, for Venus
{-4.40 max} or the full moon {-12.7)? I saw this chart:

http://www.lakeheadu.ca/~physwww/cou...b/apmagdef.gif

But it don't have the range for Venus or the Moon. I know the bright
star Alpha Carina (Canopus) has magnitude of - 0.72 which is of flux of
something like 6.8 x 10-5 W/m2. (6.8 x 10^-5 watt per squre mtre).

Since the amount of energy carried by light depends upon the
frequency, you'll need to be careful to specify the how the
magnitude is measured, that is, in what passband of frequencies.

The plot on the web page you reference is linear with the flux
on a log scale. So you have a formula something like:

m = k*log(f) where m is magnitude
f is flux watts per square meter (units
are removed for taking the log).

The information on this web page:

http://ssc.spitzer.caltech.edu/tools/magtojy/

should be enough to get you going.