Star Magnitude

By Jessica D. & Margie

Ancient Greeks invented a system so they could measure the brightness of the stars. They didn't have telescopes so their system referred to the brightness and the faintness of the stars that were visible to the naked eye.

Astronomers use the magnitude scale so that they can measure the brightness of the stars, moon, sun and any other celestial objects. Astromomers use two different methods when measuring the brightness of stars. "Apparent magnitude," which is how bright the star seems from the Earth and "absolute magnitude" or "luminosity" which means the true brightness of a star, because the brightness of stars depends on their distance from the Earth. If two stars had the same brightness but one was further away we might think that it wasn't as bright as the other one.

Astromomers noticed that stars in each brighter class (they had divided the visible stars into six classes) were about 2.5 times brighter than the stars in the previous class, so........

Class 1-Class 2 is 2.5 difference

Class 1-Class 3 is 6.25 difference (2.5^2)

Class 1-Class 4 is 15.625 difference (2.5^3)

Class 1-Class 5 is 39.065 difference (2.5^4)

Class 1-Class 6 is 97.65625 difference (2.5^5)

- If you have a negative number the flux goes up as the apparent magnitude gets smaller.

- The scale is logarithmic because it increases arithmetically while the flux decreases geometrically.