Brightness = amount of light received

Luminosity = total energy output/sec - all wavelengths

Absolute magnitude = magnitude seen @ 10 parsec distance

Apparent magnitude = brightness as seen from Earth

SPECTRAL CLASSIFICATION OF STARS

Surface
Temp
 
40,000-K         	   0 0-9                   Bluest          
      

                      B O-9

                      A O-9 

                      F O-9 

 5,700-K         	   G O-9                  Sun = G 2 

                      K >O-9 

 3,000-K          	   M O-9 >                Red

    

"Oh Be A Fine Girl (Guy), Kiss Me!"

Most stars have similar chemical composition: 91.8% H

8.0% He

0.2% The rest

HR Diagram

Absolute Magnitude vs Temperature