Surface brightness to luminosity

Warimi

Can anyone offer insight into the derivation of the surface brightness to solar luminosity conversion

S(mag/arcsec^2) = Mabs + 21.572 - 2.5log S (Solar luminosities/pc^2)

More or less my concern is the constant term, is it empirically observed value or is there a derivation for it?

thanks

mfb

The definition of magnitude and parsec are arbitrary, and if you take the log of those (multiplicative) constants and add everything you should get 21.572 in some way.

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Warimi	Surface brightness to luminosity Tweet Can anyone offer insight into the derivation of the surface brightness to solar luminosity conversion S(mag/arcsec^2) = Mabs + 21.572 - 2.5log S (Solar luminosities/pc^2) More or less my concern is the constant term, is it empirically observed value or is there a derivation for it? thanks

mfb Mentor	The definition of magnitude and parsec are arbitrary, and if you take the log of those (multiplicative) constants and add everything you should get 21.572 in some way.