Note 172 — Chapter XIII · THE NINETEENTH CENTURY. (continued 2)
Reading edition
If L be the ratio of the light received from a star to that received from a standard first magnitude star, such as Aldebaran or Altair, then its magnitude m is given by the formula
L = (1∕2·512)m - 1 = (1∕100)(m - 1)∕5, whence m - 1 = -5∕2log L.
A star brighter than Aldebaran has a magnitude less than 1, while the magnitude of Sirius, which is about nine times as bright as Aldebaran, is a negative quantity,-1·4, according to the Harvard photometry.