How do astronomers measure stellar luminosities? Measure a stars apparent brightness

and distance, then from these find its absolute magnitude which gives the stellar luminosity as the distance is removed. If the distance is unknown, it can be found from the stars temperature and radius (if these are known).

How do we measure the brightness of stars?

We measure the brightness of these stars using the magnitude scale. The magnitude scale seems a little backwards. The lower the number, the brighter the object is; and the higher the number, the dimmer it is. This scale is logarithmic and set so that every 5 steps up equals a 100 times decrease in brightness.

How do you measure luminosity?

To figure out luminosity from absolute magnitude, one must calculate that a difference of five on the absolute magnitude scale is equivalent to a factor of 100 on the luminosity scale — for instance, a star with an absolute magnitude of 1 is 100 times as luminous as a star with an absolute magnitude of 6.