1. Hertzsprung-Russell Diagram

2. Star Classification Stars can be classified in three ways:
1. Size – How massive the star is
2. Temperature – A stars color reveals its temperature.
Red stars have a cooler temperature, and blue stars have a warmer temperature.
3. Brightness/Magnitude – The amount of light a star gives off depends on its size and temperature.

3. H-R Diagram
Compares the temperature, color and luminosity (brightness) of stars on a graph.
The temperature is the surface temperature of the star
The brightness of the star is its absolute magnitude

4. APPARENT MAGNITUDE VS. ABSOLUTE MAGNITUDE
Measure of the amount of a star’s light received on Earth
Apparent magnitude
Measure of the amount of light a star actually gives off
Absolute magnitude

5. Color indicates temperature
STAR PROPERTIES
Color indicates temperature
Hot stars are
Blue
Cool stars are
Red
Medium temperature stars are
Yellow

6. Explaining the H-R Diagram
Temperature: horizontal (bottom) axis.
hotter at left
cooler toward right

7. Explaining the H-R Diagram
Brightness: vertical (left side) axis.
brightest stars near top
dim stars near bottom

8. Explaining the H-R Diagram
A star’s position on the diagram will change as it moves from its “birth” to its “death”.

9. leftover centers of old stars
White dwarfs
small, hot stars
leftover centers of old stars

10. Red-Giants
When star runs out of energy, the center shrinks and the outer part expands outward. It will grow very large and cool.

11. Supergiants
Very massive cool giant star

12. Main Sequence
Stretches diagonal from the top left to the right bottom
Our sun is an average main sequence star

13. Blue Supergiants
Very massive blue stars
Quickly use up energy and turn into Giants or Supergiants

14. Red Dwarfs
Low-mass stars
Oldest stars in galaxy

17. Explaining the H-R Diagram
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