The apparent magnitude, m, of a star measures how bright it appears from Earth. It depends on both the star's power output and its distance from us.The scale comes from the ancient Greek Hipparcos scale: the brightest stars visible to the naked eye were given magnitude 1 and the faintest visible were given magnitude 6. So a smaller magnitude means a brighter star. The modern scale extends this to very bright objects, which have negative magnitudes (Sirius: m = −1.5; the Sun: m = −26.7), and to very faint objects seen through telescopes, with magnitudes well above 6.The scale is logarithmic. It is defined so that a magnitude 1 star is exactly 100 times brighter than a magnitude 6 star. A difference of 5 magnitudes is a brightness ratio of 100, so a difference of 1 magnitude is a ratio of 1001/5 ≈ 2.51.brightness ratio = 2.51Δm where Δm is the difference in apparent magnitude. Brightness here means the intensity received at Earth.Worked example: how many times brighter is a star of m = 1 than a star of m = 4?
Δm = 4 − 1 = 3
ratio = 2.513 ≈ 16, so the m = 1 star appears about 16 times brighter.Apparent magnitude alone cannot tell you how powerful a star is: a nearby dim star can look brighter than a distant powerful one.
Δm = 4 − 1 = 3
ratio = 2.513 ≈ 16, so the m = 1 star appears about 16 times brighter.Apparent magnitude alone cannot tell you how powerful a star is: a nearby dim star can look brighter than a distant powerful one.