# Flux-Magnitude conversions

From: alistair@funge.org
Date: Fri Nov 05 2004 - 16:19:38 EST

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```I'm trying to compare my calculated flux to the magnitudes predicted by
Heaven-Above.

I've seen a number of equations to do this, but I'm not sure which one to
use.

Typical equation is:  mv = 2.5 log(F) + constant.

I'm not sure which constant to use.  I've seen several different equations,
but they vary based on wavelength band.

My understing is that apprent visual magnitude covers approximatley 0.4 -
0.7 microns.  The solar constant at these wavelengths is approximately 500
w/m^2  (0 - 0.4 microns is approx 160 w/m^2, and 0.7 - inf microns is about
700 w/m^2) Bolomteric magnitudes (all wavelengths) would use the typical
1360 or so w/m^2.

For example, if I calculate that I have 50 w/m^2 between 0.4 - 0.7 microns
at ground level, what would the mv be?

I'm trying to work backwards from a reported apparent visual magnitude to
figure out what kind of flux that is.  Then figure out what projected area
in orbit would produce this flux on the ground (taking into account
extinction).  Ultimately this projected area would then be turned into some
spacecraft geometry and varying reflectivities.

Any help would be appreciated.

Alistair
Dayton

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