# Hr diagram – plotting the stars

### Instructions:

You will be using Table 1 and Table 2 to plot the 20 nearest and 20 brightest stars on the attached HR diagram.  The following tips will be helpful when graphing stars;

• Temperature is on the horizontal axis, absolute magnitude is on the vertical axis,
• Absolute magnitude decreases as the values become more positive,
• Notice the graph lines used to plot temperature are unevenly spaced and that the number of Kelvins between each line is not constant.  Carefully check a star’s temperature and the value of its graph line before plotting each star.
• Use a plus sign (+) to graph each of the nearest stars (listed in Table 1) on the diagram.

Use a circled dot (o) to graph each of the brightest stars as seen from Earth (listed in Table 2) on the diagram.  Show stars that appear on both tables using a square ().  Please sign you name on your graph and include the date.

Table 1. The 20 Nearest StarsNameDistance (Parsecs)Temperature KAbsolute MagnitudeAlpha Centauri

1.31

5,800

+4.4

Barnard’s Star

1.83

2,800

+13.2

Wolf 359

2.35

2,700

+16.8

Lalande 21185

2.49

3,200

+10.5

Sirius

2.67

10,400

+1.4

Luyten 726-8

2.67

2,700

+15.4

Ross 154

2.94

2,800

+13.3

Ross 248

3.16

2,700

+14.7

Epsilon Eridani

3.30

4,500

+6.1

Ross 128

3.37

2,800

+13.5

Luyten 789-6

3.37

2,700

+14.9

61 Cygni

3.40

2,800

+7.5

Procyon

3.47

6,800

+2.7

Epsilon Indi

3.51

4,200

+7.0

Sigma 2398

3.60

3,000

+11.1

BD +43o44

3.60

3,200

+10.3

Tau Ceti

3.64

5,200

+5.7

CD -36o15693

3.66

3,100

+9.6

BD +5o1668

3.76

3,000

+11.9

CD-39o14192

3.92

3,500

+8.7

The 20 Brightest Stars

Name

Distance

(Parsecs)

Temperature

(K)

Absolute

Magnitude

Sirius

2.7

10,400

+1.4

Canopus

30.0

7,400

-3.1

Alpha Centauri

1.3

5,800

+4.4

Arcturus

11.0

4,500

-0.3

Vega

8.0

10,700

+0.5

Capella

14.0

5,900

-0.7

Rigel

250.0

11,800

-6.8

Procyon

3.5

6,800

+2.7

Betelgeuse

150.0

3,200

-5.5

Achernar

20.0

14,000

-1.0

Beta Centauri

90.0

21,000

-4.1

Altair

5.1

8,000

+2.2

Alpna Crucis

120.0

21,000

-4.0

Aldebaran

16.0

4,200

-0.2

Spica

80.0

21,000

-3.6

Antares

120.0

3,400

-4.5

Pollux

12.0

4,900

-0.8

Fomalhaut

7.0

9,500

+2.0

Deneb

430.0

9,900

-6.9

Beta Crucis

150.0

22,000

-4.6

### Analysis and Conclusion:

Type your answers to the below questions in your lab report. Based on the results of the HR diagram you have created, answer the following questions.  For all answers use complete sentences. After you have completed the below questions, scan or take an image of your HR graph and insert it into your lab report, making sure that it is clear and readable. Make sure to provide any/all sources used.

1. Compare the two star lists.  Name any stars that happen to appear on both lists.
2. What does your answer to Question 1 indicate about the nearest stars?  Are the nearest stars also the brightest stars as seen from the Earth?
3. A star located in the lower right portion of the diagram is cool and dim.  What are the characteristics of a star in the upper left of the diagram?  What are the characteristics of a star in the upper right of the diagram?
4. Refer to the HR Diagram of your textbook or other source.  To which group do most of the stars on your diagram belong?
5. According to your diagram are any of these stars white dwarf stars?  What is the evidence for your answer?
6. Our Sun has a temperature of 6,000K and an absolute magnitude of +4.7.  Use an asterisk (*) to show the location of the Sun on your diagram.  To which group does the Sun belong?
7. In a paragraph of 2-3 sentences compare the absolute magnitude and temperature of the Sun with those of other stars in its group.
8. Betelgeuse is 150 parsecs away and has a surface temperature of only 3,200K yet Betelgeuse is one of the brightest stars as seen from the Earth.  What does this indicate about the size of Betelgeuse?  Is your answer supported by the location of Betelgeuse on the diagram?
9. On your diagram there is another star plotted near Betelgeuse.  What is the name of this star?  What kind of star is it?
10. Compare our Sun with stars that are considered to be Red Giants.  Which star is further along in its life cycle?  How do you know?

## II. HR Diagram Simulation. Evolution of the Sun.

Follow this link to the Hertzsprung-Russell Diagram Explorer simulation. (Please try using Explorer, or Firefox browsers.  Note that when using these browsers you will need to allow Adobe-Flash to run, and there might be plugins as well.  This is very safe & trusted software. For example, look up in the web address bar and see if the plug-in manager has come up example, and you might need to click on that to allow the app to open. The direct site you are going to is: HR Simulation .)

When you open the simulation you will see an image of two stars, one labeled star and one labeled sun.  The default setting when you open the simulation is for the star to have the same settings as the Sun for all values of temperature, luminosity, and radius. (T = 5,800K, L = 1sun, R = 1 sun).  You can change the settings in various ways, clicking on the slider bars for temperature and luminosity, or clicking on various spots on the HR diagram to move the red crosshair shown on the diagram. (Below is a screenshot of the Hertzsprung-Russell Diagram Explorer.)

To start this activity check all four of the boxes under options so they will be seen on the HR diagram.  You will now be asked to navigate through the simulation and answer questions on what you see.  You will also be asked questions for which you will need to consult other sources.

### Navigating the HR Diagram Simulation:

1. Under Plotted Stars click on the button to display the “nearest stars.” Describe the relationship in terms of temperature, luminosity, and radius of the nearest stars to the location of the Sun on the diagram. Which luminosity group(s) do these stars lie in?
2. Again, under Plotted Stars click on the button to display the “brightest stars.” Describe the relationship in terms of temperature, luminosity, and radius of the nearest stars to the location of the Sun on the diagram. Which luminosity group(s) do these stars lie in?

The next series of questions will ask you to move the red crosshairs on the diagram to different spots within the diagram to understand the evolution of our Sun and the changes that it will experience with time.

1. The Sun as it ages will grow in size and move off of the main sequence into an area of the diagram called the “instability strip.” Move the crosshair into the instability strip so it is approximately in the middle of the group. Describe the changes that will occur with the Sun in terms of color, temperature, luminosity, and radius.
2. Why will the Sun move off the main sequence into the Instability Strip? (You will need to consult other sources for this answer; supply any references used.)
3. What type of stars are currently stars that would be found in the instability strip? (Again, consult other sources.)
4. The next stage in the life of the Sun as it ages is the “Red Giant” luminosity class. Move the crosshair to the Red Giant class (a good spot would be just above the “an” in the word Giant). Describe the changes that will occur with the Sun in terms of color, temperature, luminosity, and radius.
5. The last stage in the life of the Sun as it ages is the “White Dwarf” luminosity class. Move the crosshair to the White Dwarf class (a good spot would be just above the “s” in the word Dwarfs). Describe the changes that will occur with the Sun in terms of color, temperature, luminosity, and radius.
6. As a White Dwarf the Sun has decreased significantly in size. What happened between the Red Giant and White Dwarf classes to cause this? (Consult outside sources.)
7. Our Sun, however, is not big enough to be a Super Giant star, this only happens to the very highest mass stars.  Move the crosshair back to the main sequence but to an area of R=10sun  (a good spot would be just above the “rf” in the word Dwarfs). Describe the differences between this star and our Sun in terms of color, temperature, luminosity, and radius.
8. This star, from Question #9, will become a Super Giant. Move the crosshair into the “Super Giant” class  (a good spot would be just above the “gi” in the word Supergiants). Describe the differences with this star in terms of color, temperature, luminosity, and radius.
9. In a paragraph (minimum of 50 words) summarize what you have learned from both Parts 1 and 2 of this laboratory activity. What are some implications for the Earth as the Sun ages and moves through the different phases of its evolution?
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