Magnitude

An adopted arbitrary geometric scale whereby to indicate the brightness of a celestial object; according to which an increase of 5 magnitudes corresponds to 100-fold decrease in brightness. Apparent Magnitude As it actually appears - ranging from -26.7 for our Sun to + 20 for the faintest stars which can be photographed by the largest telescope. Absolute Magnitude. As it would be perceived if removed to a point from which its parallax would be 0.1" of arc - ranging from -5 for the brightest of stars to +15 for the faintest, with our Sun about +5. The faintest star visible to the unaided eye is of the sixth magnitude. Since greenish yellow registers best on the eye and blue-violet registers best on the photo-plate, magnitudes vary somewhat according to the method of observation employed.