# Flux & apparent magnitude

by Schmetterling
Tags: apparent, flux, magnitude
 P: 31 How to calculate the visual magnitude of a star having only the flux of such star? The equation involves 2 magnitudes and 2 fluxes, corresponding to 2 objects a and b: ma-mb= -2.5log10$\left( \frac{F_a}{F_b}\right)$ but I just have Fa and I have to obtain ma. Is it valid to take ma=-2.5log10 Fa?
 HW Helper Sci Advisor Thanks P: 9,002 the "b" indexed values would have to be some reference value that depends on the scale you are using. http://en.wikipedia.org/wiki/Apparen...ference_Values
 P: 31 Ok, but in that table the values for "m" don't appear, only the fluxes :-s
HW Helper
Thanks
P: 9,002

## Flux & apparent magnitude

 Ok, but in that table the values for "m" don't appear
... yes they do: right at the top of the 4th and 5th columns where it says "m=0". But you can use any reference values that make sense in terms of your coursework.
Specifically: you should not get your reference-values off wikipedia. You must have access to a library or a text book or something like that?
In a pinch - go to wikipedias primary source.

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