Stars are classified by their spectra and their temperature.
The 7 main types of stars are O,B,A,F,G, K, and M. A easy way to remember the order of the letters is, ''Oh be a fine guy/girl, kiss me."
A dwarf star is 20 times bigger then our sun and it's 20,000 times brighter.
The characteristics to classify how old or how young the star is color, temperature, size, composition and brightness
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