1. Hertzsprung-Russell Diagrams
Astronomy

2. An H-R Diagram Based on Hipparcos Data

3. A Modern Version of the H-R Diagram

4. GENERAL INFO:
Plot of luminosity vs. temp or by absolute magnitude vs. spectral class
90% of stars are in a band called the main sequence (our sun is in middle)
Other 10% are in upper right and lower left

5. Blue giants--
upper left part of main sequence
BIG, luminous, hot
Examples: Rigel

6. Red dwarfs--
lower right portion of main sequence
little, faint, cool
Examples: Barnard’s star

7. White dwarfs--
lower left group OFF of the main sequence
little, faint, hot
Examples: Sirius B

8. Red Giants--
upper right portion OFF the main sequence
big, luminous, cool
Examples: Arcturus, Aldeberan

9. Red Supergiants--
same as red giants, just bigger
Examples: Betelgeuse, Antares

10. The Mass-Luminosity Relation for
Main Sequence Stars

11. A star’s position on the main sequence is determined by its MASS.
Most massive stars are most luminous
largest mass of a stable star is ~100 x sun
faintest red dwarfs are 1/10 sun’s mass
brown dwarf: too small to be a star (almost like Jupiter)

12. Most stars are…
Red giants
White dwarfs
Red dwarfs
Blue giants
Main sequence stars

13. Blue giants?
Red giants?
White dwarfs?
The sun?
Red dwarfs? E

14. Blue giants are…
Hot or cool?
Big or small?
Bright or faint? E

15. Red giants are…
Hot or cool?
Big or small?
Bright or faint? E

16. White dwarfs are…
Hot or cool?
Big or small?
Bright or faint? E

17. Our sun is…
Hot or cool?
Big or small?
Bright or faint? E

18. Red dwarfs are…
Hot or cool?
Big or small?
Bright or faint? E