The Magnitude Method

The intensity of light coming from a star decreases as the distance bewteen us and the star increases. See animation opposite. Right click on the image and choose reload to see it again. 

Using the Russell-Hertzsprung diagram, we can tell from the colour of light coming from a star how bright it would be if it were near. 

Astronomers construct graphs like the one opposite using stars of the same type whose distance and brightnesses are known. 
Then the graph can be used to find the distance of stars whose apparent brightness can be measured.  
Show the maths. 
 
 

Animation by S.Mack & Gif Movie Gear
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