H-R Diagram of Star Clusters pre-lab handout 2017 (rev) (2)...

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The Hertzsprung-Russell Diagram of Star Clusters1One of the most useful tools the astronomer has for studying the evolution and the ages ofstars is the Hertzsprung-Russell or H-R Diagram (Figure 1), sometimes loosely called a Color-Magnitude diagram.This is basically a graph of the surface temperature versus the luminosity ofstars, on which we plot the characteristic values of surface temperature and luminosity for asingle star or a group of stars.A sample H-R diagram is shown in the figure below.Note thatthe stars with lower temperatures are on therighthand side of the H-R Diagram, so thattemperature increases towards theleft.Figure 1: The H-R DiagramA star’s luminosity (or Absolute Magnitude) and temperature (or spectral type or B-Vcolor index) determine its position of the H-R diagram. As you can see from the diagram above,the hottest, most luminous stars lie at the upper left of the diagram, and the coolest, dimmeststars lie at the lower right. Stars at the upper right are extraordinarily luminous despite havinglow surface temperatures, and so they must have huge surface areas---their radii can be athousand times bigger than the sun.These are calledred giants. Stars at the lower left of thediagram are exceptionally faint even though they are very hot, so they must be small---their radiiare typically a hundred times smaller than the sun, or about the size of the earth. They are calledwhite dwarfs.Most stars are found along the line running from the lower right to the upper leftof the H-R diagram, a region called the

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Term
Fall
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Tags
Astronomy, Stellar Evolution, Stellar classification, main sequence, H R Diagram

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