1. Stars

2. Different colors of gas denote different temperatures
Color of stars
Different colors of gas denote different temperatures
EX: flames in a fire can tell you the parts of the flame that are hotter than other parts
White and clear blue are hotter than yellow

3. Composition of Stars Spectrum- rainbow of colors
Spectrograph – an instrument used by astronomers to spread starlight out into its colors (similar to a prism)
Stars are made of various gases that produce different spectrum of light

5. Classifying stars
Stars are classified by how hot they are (temperature) and luminosity (brightness)

6. How bright is that star?
Magnitude is used to indicate how bright one object is compared with another
A smaller number means a brighter star
EX: Our sun is about +5. A blue star, which are the brightest, have an absolute magnitude of -10
Also used to show brightness of astronomical objects
Venus shines with an apparent magnitude of 4.6
Full moon shines with an apparent magnitude of -12.5

7. Distances to the stars
Light-year: distance light travels in one year
Speed of light is ~300,000km/s (186,000mi/s) or 9.5 trillion km in one year
Easier to use light year than km/s
North Star is 431 light years away, or 4,080,000,000,000,000km

8. Motion of the Stars
Due to Earth's rotation, we see the sun rise and set, and stars come and go in the night
Stars do move in space, but because they are so distant, their motion is hard for us to measure
Over thousands of years, their movement would be obvious

9. H-R diagram
1911, Danish astronomer Ejnar Hertzsprung plotted the temperature and brightness of stars on a graph
1913, American astronomer Henry Norris Russell made similar graphs
Although they used different data, they came up with the same graphs
Hertzsprung-Russell (H-R) diagram

10. H-R Diagram

11. When stars get old
Most stars stay in main sequence for a long time, but not forever
Average stars (our sun) turn into red giants and then white dwarfs
More massive stars may explode and become violent – supernova

12. Supernova Death of a large star by explosion
After the explosion, two things can happen
Neutron star (pulsar – spinning neutron star)
Black holes

14. Black Holes
An object with more than three solar masses squeezed into a ball. So small and massive and its gravity is so strong that not even light can escape
Doesn't gobble up other stars, but can pull in material from the nearby star