1. H-R Diagram

2. Star Brightness
Luminosity: the total amount of energy emitted by a star per unit time
Measured in joules per second or watts
Like a lightbulb!

3. Magnitude: logarithmic measure of brightness
Apparent magnitude (m): brightness as it appears from earth
Absolute magnitude (M): intrinsic brightness of an object as it would appear if all objects were the same distance from earth
Smaller numbers = brighter!
If you know the m (which we can measure directly), you can calculate the M if distance (d) is known:

5. 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

7. Which is hotter?
main sequence white dwarf

8. Answer: white dwarf

10. Trends….. 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

11. Arrival on the Main Sequence
The mass of the protostar determines:
how long the protostar phase will last
where the new-born star will show up on the Main Sequence
i.e., what spectral type the star will have while on the main sequence