1. Stars and HR Diagrams

2. What is a star? Gases and radiant energy (heat and Light)
Vary in color (red, blue, orange, yellow)
Vary in size (12 km – 1,392,000,000 km)
Vary in mass (1/50th – 50X the sun)

3. What is our Sun? A star Medium sized, or main sequence star
1,392,000 km
330,000 more massive than earth

4. How to tell elements Before Hubble telescope used: Spectrometer
Device used to analyze light from stars
Separates light wavelengths
Like a prism

5. Star Composition Discover by dark-line spectra
Different lines for every element in the star
Stars are composed of elements found on earth
Hydrogen and Helium are the most common in stars

6. Star temperature Indicated by color: Blue= hot (10,000 to 50,000 C)
Yellow=middle (4,000 to 10,000 C)
Red= coolest (2,800 to 4000 C)
Steel melts at 1300 C

7. Star Motion Two types Apparent Actual Motion visible with unaided eye
Move westward around polaris (N. Star)
Earth Rotating
See different stars in different seasons
Earth Revolves around the sun
Actual
Rotate on axis
Revolve around another star
Move away or towards earth

8. Star Movement and Distance
Circumpolar- star that are always overhead (North Star, Big Dipper, Little Dipper)
Parallax- distance determined by star movement in the sky measure over 6 months
Big Shift= close to earth
Hardly Moves= far star
Red Shift and Blue Shift
Look at the spectrum of the stars
Red Shift stars are moving away from earth
(long wavelengths of light)
Blue Shift stars are moving towards the earth
Shorter wavelengths of light)

9. Star Distance Light Years: Distance light travels in a year
Speed of light is 300,000 km/s or 670,616,629 miles per hour
Sunlight takes about 8 minutes to get from the sun to here.

10. Star Brightness Two scales: Apparent Magnitude
How bright a star APPEARS on earth
Bright stars (low #’s), dim stars (high Numbers)
Can have negative numbers (planets, sirius)

11. Star Brightness Cont. Absolute Magnitude Nearby Stars- Far Stars-
How bright a star ACTUALLY is
Measured from 32.6 light years away from earth
Nearby Stars-
Lower number apparent magnitude than absolute magnitude.
Appear brighter because they are closer
Far Stars-
Higher number apparent magnitude than absolute magnitude
Appear dimmer than they actually are

12. Star Classification Hertzsprung Russel Diagram (H-R Diagram)
Surface temp vs. absolute mag.
Brightness increases as Temp increases

15. Groups on H-R Main sequence stars Middle band, Visible
Giants-cool, bright, because large
Super Giants- very cool, bright, large
White Dwarfs- hot, dim, because small