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The HR Diagram. The Hertzsprung Russell diagram –HR Diagram. 90% of stars are found on a diagonal line called the main sequence Hotter on the left cooler on the right Brighter at top dimmer at bottom. Groups of Stars. Main sequence—diagonal line Red Giants– bright and cool
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The Hertzsprung Russell diagram –HR Diagram • 90% of stars are found on a diagonal line called the main sequence • Hotter on the left cooler on the right • Brighter at top dimmer at bottom
Groups of Stars • Main sequence—diagonal line • Red Giants– bright and cool • Supergiants—brighter and cooler • White Dwarfs—dim and hot
Color and Stars Think of a candle • Hottest part is blue • Red is the cool part at the top Color indicates temperature
Annie J Cannon (1863-1941) Spectral Class • OBAFGKM • Oh Be A Fine Girl Kiss Me • Indicates a stars composition
All Types of Stars • Recall - • Stars have Differentcolors • which indicate different temperatures
All Types of Stars Out Beyond Andromeda, Fiery Gases Kindle Many Red New Stars Oh! Be a Fine Girl - Kiss Me Right Now Sweetheart ! Oh! Be a Fine Girl - Kiss Me !
Star classification • If we look at a star with a spectroscope we see dark lines called absorption spectra • These lines indicate the stars chemical composition
Absolute vs. Apparent Magnitude Absolute —how bright a star actually is Apparent—how bright it appears from Earth
Revisit the HR diagram • Where are stars most of their lives? • Where are they when they begin to die? • What are they after they use up their fuel?