Re: Magnitude comparisons

Sue J. Worden (worden@uts.cc.utexas.edu)
Sat, 5 Dec 1998 11:32:46 -0600 (CST)

Ron Lee wrote:
> 5 magnitudes = 100 times difference in brightness

Ignoring units/conversions and constants for the purpose of
comparing the relative brightness of two objects:

   Magnitude : - log (base 5th root of 100) of Brightness

   (100)^(1/5) = 2.5118864315...

Or:

   Brightness : [ (100)^(1/5) ]^(-Magnitude)

Or to compare two objects:

   Brightness_2
   ------------  =  [ (100)^(1/5) ]^[ Magnitude_1 - Magnitude_2 ]
   Brightness_1

So for an Iridium flare at magnitude -8 compared to a nominal
Jupiter at magnitude -2.5:

   Iridium Brightness
   ------------------  =  [ (100)^(1/5) ]^[ -2.5 - -8 ]  =  158.49
   Jupiter Brightness

Or the Iridium flare was about 160 times brighter than Jupiter.

--Sue (worden@uts.cc.utexas.edu)