1. H-R Diagrams

2. An H-R Diagram is… A graph of stars’ BRIGHTNESS and TEMPERATURE
It also shows color since color is related to temperature
It was made by two astronomers who plotted the data for thousands of stars and noticed some trends.
It stands for Hertzsprung-Russell Diagram

4. Notice….. Temperature DECREASES as you move to the Right on the X-axis
Absolute Magnitude INCREASES as you move up on the Y-axis.
NEGATIVE absolute magnitude values are BRIGHTER than POSITIVE absolute magnitude values

6. A star…
Starts off in the lower right hand corner in MAIN SEQUENCE when it first becomes a star.
As it gets hotter and brighter, it moves up the main sequence.
Then it moves to upper right section when it changes to Giants/Supergiants.
It ends in the lower left section when it changes to a white dwarf

9. Questions
What is the relationship between temperature and brightness for a main sequence star?
What kinds of stars are the hottest?
What kinds of stars are the brightest?
Why do White dwarves have a low brightness when they are so hot?

11. Questions 6. What is the temperature of the sun?
5. Why do Giants have such high brightness when they are not especially hot?
6. What is the temperature of the sun?
7. What is the absolute magnitude of the sun?