3 Chapter 3 – Are there different types of stars?
OpenStax Astronomy Chapter 17: The Brightness of Stars
OpenStax Astronomy Chapter 18: The Stars: A Celestial Census
Spectral Types
I.
A. Stars are according to their
B. lines in spectra tell us what are there and surface
C. From to the spectral types are:
1. Types further divided by number, 0-9
2. is type (Temp is about 6000 K or 10,000° F)
3. To memorize try: Oh Be A Fine Guy/Gal Kiss Me or Only Bored Astronomers Find Gratification Knowing Mnemonics
D. Spectral , , and surface are all directly related, if know one then know all
E. stars: type , greater than K,
F. : type , about K,
G. stars: type , less than K,
HR Diagram
II.
A. Developed by and (early 20th century)
B. stars on diagram to:
1. or learn about a star (type, size, mass, etc.)
2. Better understand stellar (how stars with time) of different types of stars
C. Usually plot of vs. surface
1. Luminosity on with a logarithmic scale (factor of 10)
a. Can also plot on y-axis because depends on luminosity
2. Surface Temperature on , from to (left to right) with a non-linear scale
a. Can also plot (blue to red) or (OBAFGKM) on x-axis
D. of HR Diagram = Most stars
E. side =
F. Size: Diagonally and means diameter
1. stars (giants) in upper right corner
G. (MS): where stars (90%), including the , are on the HR diagram
1. Runs diagonally from upper to lower
2. Runs from , luminous stars to cool, stars following the types in order (OBAFGKM)
H. The of a star determines its on the MS
1. Mass and both as you go “down” the MS (left to right)
I. All stars on the MS are fusing into helium in their cores
J. stars begin their life on the MS, but stars at stages of evolution are on the MS
1. or Supergiants: big, cool but very luminous (upper right of HR)
2. : small, hot with very low luminosity (bottom left)
The two axes on the Hertzsprung-Russell (H-R) diagram can be
A. luminosity and temperature
B. apparent magnitude and absolute magnitude
C. radius and main sequence
D. radius and luminosity
E. spectral type and temperature
III. of Stars
A. If know luminosity and temperature, we can the (diameter) of a star
1. Or plot it on the to figure out size
2. A star is always or dense
B. A and star is more (gives off more energy) than a small cool one
1. Sizes of stars range from about 0.1 to more than times the size of the Sun
C. If two stars have temperature, but one has a luminosity, it must be
If two stars have the same temperature, but Star Jack is more luminous than Star Jill, which of the following is true?
A. Jack is bigger than Jill
B. Jill is bigger than Jack
C. Jack and Jill are the same size
D. There is no way to tell which star is bigger.
If two stars have the same size, but Star Alpha has a higher surface temperature than Star Beta, which of the following is true?
A. Alpha is more luminous than Beta
B. Beta is more luminous than Alpha
C. Alpha and Beta have the same luminosity
D. There is no way to tell which star is more luminous.
Look at the HR diagram. Which star is larger, X or Y?
A. X is larger
B. Y is larger
C. Same size
D. No way to tell
Tutorial Activity – HR Diagram
For this activity, you may want to use a separate sheet of paper. Have your drawing fill the entire page.
1. Draw and label the x- and y-axes of an HR diagram. Include any properties of start that can be plotted on that axis. Make your axes fill the space, you will be adding more to the diagram!
2. Draw the Main Sequence. Label the parts of the MS where the high-mass and low-mass stars are.
3. Label the part of the HR diagram where you would find the biggest (giant and supergiant) stars.
4. Label the part of the HR diagram where you would find the smallest white dwarf stars.
5. Label the part of the HR diagram where the brightest (most luminous) stars are.
6. On the x-axis, label where the hottest and coolest stars should be.
7. On the x-axis, label where the blue stars are and where the red stars are.
