|This is a measure of the brightness of a celestial object. The
lower the value, the brighter the object, so magnitude -4 is
brighter than magnitude 0, which is in turn brighter than
magnitude +4. The scale is logarithmic, and a difference of 5
magnitudes means a brightness difference of exactly 100 times. A
difference of one magnitude corresponds to a brightness
difference of around 2.51 (the fifth root of 100). The system
was started by the ancient Greeks, who divided the stars into
one of six magnitude groups with stars of the first magnitude
being the first ones to be visible after sunset. In modern
times, the scale has been extended in both directions and more
strictly defined. Examples of magnitude values for well-known
objects are; |Sun||-26.7 (about 400 000 times brighter than full
Moon!)| |Brightest Iridium flares||-8| |Venus (at
brightest)||-4.4| |International Space Station||-2| |Sirius
(brightest star)||-1.44| |Limit of human eye||+6 to +7| |Limit
of 10x50 binoculars||+9| |Limit of Hubble Space Te