magnitude, Pogson 
The Pogson magnitude is the standard astronomical magnitude system, where one
increment in magnitude is an increase in brightness by the fifth root of 100.
A star of 1st magnitude is therefore 100 times as bright as a star of 6th magnitude. Mathematically this is expressed as
M1  M2 = 2.5log(F1/F2)
where M1 and M2 are the magnitudes of two objects, and F1 and F2 are their luminous fluxes.
