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Transcript
The Hertzsprung-Russell Diagram Organizing Star Property Data The H-R Diagram The “H-R” Diagram was invented around 1910 to organize stars based on their properties. The diagram is a graph. Vertically the scale is increasing Luminosity Horizontally the scale is Spectral Class/Temperature From Hot (O class) to Cool (M class). H-R Diagram Notice there are 4 groups: Most Stars are “Main Sequence” Others are: White Dwarfs, Giants and Supergiants About the Groups Most stars lie in the main sequence because if a star is hotter it is brighter. Thus you would expect stars of the same size but different temperatures to form a diagonal line since “hotter means brighter” That Main-Sequence is steeper than a ‘same-size diagonal” shows that larger mass ‘normal’ stars are hotter…and thus ‘burn’ fuel fast, and have short lives White Dwarfs are hot, but not that bright, so they must be small. Giants and Supergiants are cool, but bright so they must be very large. The Instability Strip On the H-R Diagram Cepheid & RR Lyrae Variable Stars are found in an area called the “Instability Strip”
