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The Hertzsprung-Russell Diagram

The Hertzsprung-Russell Diagram. What is the HR Diagram?. Tool that shows relationships and differences between stars. Relative measure of luminosity & temperature. Shows stars of different ages/stages at the same time. The Basics…. Each star is represented by a dot.

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The Hertzsprung-Russell Diagram

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  1. The Hertzsprung-Russell Diagram

  2. What is the HR Diagram? • Tool that shows relationships and differences between stars. • Relative measure of luminosity & temperature. • Shows stars of different ages/stages at the same time.

  3. The Basics… • Each star is represented by a dot. • Vertical axis shows luminosity/absolute magnitude. • How much energy a star radiates in 1 sec. • How bright/dim a star appears, compared to Sun • Horizontal axis shows surface temperature (in K.) • NOTICE: Goes from high temps at left side to lower temps at right side!

  4. Let’s Practice… http://sunshine.chpc.utah.edu/Labs/StarLife/support/HR_init.swf

  5. Types of Stars • Stars that fit the expected pattern – cool and dim; hot and bright – are called main sequence stars • Most stars fall in the region called main sequence. • Curved line sloping from top left to lower right of HR diagram.

  6. Why is there a “main sequence”? • Usually there is a predictable relationship between brightness and temp. Hotter things are brighter Hotter temp = more energy is radiated. Bigger stars are brighter. Bigger surface area = more energy radiated.

  7. Exception to the rule! • Some stars are cool but if they are massive enough, they can have high luminosity  red giants or supergiants

  8. Another Exception to the Rule • Some stars are very hot and shine intensely but are small so they don’t radiate much energy (appear dim)  white dwarf stars

  9. Let’s see how a star changes throughout its life… http://sunshine.chpc.utah.edu/Labs/StarLife/support/HR_animated.swf

  10. More Practice! http://sunshine.chpc.utah.edu/Labs/StarLife/support/HR_static.swf

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