# Tag Info

$\mu_{B}$ is surface brightness of an extended source in the B-band. This is given as (apparent) magnitude per square arc seconds. You need to calculate the area you observe at the distance R through an angle of 1 X 1 arc seconds. With some trigonometry applied you will get; $$A = 4 R^{2} \frac{1 - \cos \varphi}{1 + \cos \varphi}$$ Where the angle is 1''. ...