Name: _________________
H-R Diagram
The Hertzsprung-Russel Diagram is as important to astronomers as the Periodic Table of the Elements is to chemists. It is a plot of luminosity (L) as a function of temperature (T). Practically, we measure absolute magnitude (M in general, B in blue, V in visible) instead of luminosity, and color (B-V) instead of temperature. (Temperature, color, and spectral class are all related.) Don’t forget that a large number for magnitude means a dim object, while a small number means it is bright.
Table of Brightest Stars
Table of Closest Stars
Computer with MS Excel –or– graph paper and pencil
Look at the data table titled “Brightest Stars.” Open Microsoft Excel and enter this data (or only the relevant columns) into a table. Then make a plot of the data, with B-V along the horizontal (x) axis, and absolute magnitude along the vertical (y) axis. If you don’t know how to do this, ask your teacher for help. If your class is using graph paper, you can instead graph by hand.
Make sure to save often, label your axes, and put your name on your graph. After creating the graph, print a copy and answer the following questions.
If you have a large number for B, is the star bright or dim in Blue?
If you have a small number for V, is the star bright or dim in Visible (green light)?
When you have a large B-V, is the star brighter in the Blue or Visible? Explain why.
Describe the appearance of the graph in words. What is the overall shape of the graph? Are the stars clumping together anywhere?
Which types of stars are the most common? (Bright or dim? Blue or red?)
Astronomers often talk about “representative samples.” A representative sample of stars is an average group of stars, ones that can show the astronomer what all stars are like. For example, if you wanted to study all people, you wouldn’t want to only look at girls aged 12.
Do you think this sample of 26 stars is a representative sample? Why or why not?
Now look at the data table titled “Nearest Stars.” Enter the data into MS Excel and save, graph, and print as before.
What is different about this plot and the previous one?
Which types of stars are the most common? (Bright or dim? Blue or red?)
Do you think this sample of 30 stars is a representative sample? Why or why not?
Label the Main Sequence and Red Giant Branch on both your graphs.
The closest and brightest star was actually omitted from the two data tables. What star is that?
Why might we have chosen to omit it?