Exam 2: Stars (take home test)

Name ___________________________________

Star Name _______________________________
Score _______________

Date: ________________


Each of you has your very own star. By the end of this exam, you be an Astronomy 101U/V expert on that one star. I expect your work to be complete, accurate, and above all, representative of your best effort. Answer all questions as specifically as possible. Most answers should involve only a few, succinct sentences; you do not have room for much verbal rambling. Supply all information in the spaces provided on these sheets. Please make sure I can easily read your writing; otherwise, I will assume you really didn't want me to.

In some cases, you will have to estimate some qualities or quantities for your star. (For example, you cannot find any definite information about the evolutionary stage of your star. Would a star of exact or similar spectral type and luminosity class do as a reference?) As is the case for the labs this quarter, just make sure that you spell out the logic you used. Original and/or sound reasoning is just as important as getting the "right" answer. You may find conflicting values for your star in the sources you use. Please reference all sources in your work.


Constellations and an alphabetical star list by Chris Dolan.
Portraits of Stars and Their Constellations, by Dr. James B. Kaler.
More Star names and constellations, this time from Sky Eye.
A listing of stars from Your Sky that includes Bayer Designation ("Identity") and star fields.
A complete listing of the types of telescopes for different wavelengths is given in More about Electromagnetic Radiation from Imagine Universe.



The book has figures that will tell you the approximate numbers to use:


  1. Identifying Your Star

    (5 pts) Find a star map of your constellation and reproduce that map here. Include at least 4 named stars (Bayer designation is OK). Show the outline of the constellation and identify which star is your star.

  2. Stellar Parameters(8 pts)

    (Note: when you see "magnitude" in your references, that means apparent magnitude.
    Star Name Bayer

  3. Observing your Star

    1. (2 pts) Which season would be the best one for observing your star? (Pick the one where it is in the night sky for the most hours -- your text has star maps.)

    2. (2 pts) Calculate the wavelength (or use the appropriate figure in the book) at which your star radiates most of its energy (peak wavelength of the star's thermal radiation). Show all work or reference the figure you used.

    3. (4 pts) Consider the wavelength at which your star radiates most of its energy. What orbiting telescope should you choose to apply for time? Explain your answer.

  4. The Evolution of Your Star

    (9 pts)Reproduced here is Fig. 14.15 of your text.
    1. Fill in the life track of a 1 solar-mass star from main sequence to red-giant stage.
    2. Do the same for a 3 solar-mass star and a 6 solar-mass star assuming the evolution off of the main sequence retraces their birth path to the main sequence (Fig. 14.8).
    3. Using the spectral type and luminosity class of your star, locate your star on this graph.
    4. What is the mass of your star? (Give your source or how you figured out the mass.)

    5. Every quantity has an uncertainty attached to it. What is the uncertainty in the mass of your star? What logic did you use in arriving at this number?

    6. Based on the mass of your star and where your star is on the HR Diagram:
      • (2 pts) Approximately how long did (will) your star spend on the main sequence? (Show all work or reference the figure used.)

      • (2 pts)What is probably happening in its core? How is the core being supported?

      • (2 pts)How is the rest of the star being supported?

      • (2 pts)What is probably the next stage for your star?

      • (2 pts)How will your star finally die?

      • (5 pts)Find something astrophysically (that is, having nothing to do with mythology or astrology) notable about your star. State it here and then explain it to your non-science roommate.

      • (10 pts)List and briefly explain 5 of the steps in the formation of our solar system.

      • (5 pts)In general, how would this scenario differ if the Sun were, say, 20 times its present mass?

      • (12 pts)You are embarking on a remarkable journey to the center of the Sun. Starting with the corona, describe one identifying feature for each region of the Sun. State how the radiative energy is getting through each region.

      • (6 pts)Through gravitational equilibrium, the Sun self-regulates itself so well that we notice only a tiny variation in its luminosity over decades of observing.
        1. Explain what happens in the Sun if the radiative pressure becomes greater than the opposing force of gravity.

        2. Explain what happens in the Sun if the force of gravity becomes greater than the opposing radiative pressure.

      • (11 pts)Know Your Stars! Consider the following data table for the 15 brightest stars in the sky.

        The 15 Brightest Stars

        Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)

        BSC No. Name (ID) Apparent
        Parallax (arcsec) Spectral Type
        Luminosity Class
          Sun (Sol) -26.00   G2 V 4.75
        2491 Sirius -1.46 0.375 A1 V 1.41
        2326 Canopus -0.72 0.028 F0 II -3.48
        5340 Arcturus -0.04 0.090 K1.5 III -0.27
        5459 Rigil Kentaurus -0.01 0.751 G2 V 4.37
        7001 Vega 0.03 0.123 A0 V 0.48
        1708 Capella 0.08 0.073 G5 III + G0 III -0.60
        1713 Rigel 0.12 0.013 B8 I -4.31
        2943 Procyon 0.38 0.288 F5 IV 2.68
        0472 Achernar 0.46 0.026 B3 V -2.47
        2061 Betelgeuse 0.50 0.005 M1 I -6.01
        5267 Hadar 0.61 0.009 B1 III -4.62
        7557 Altair 0.77 0.198 A7 V 2.25
        1457 Aldebaran 0.85 0.048 K5 III -0.74
        6134 Antares 0.96 0.024 M1.5 I + B4 V -2.14
        (1 pts) Which star has the greatest luminosity?
        (1 pts) Which star has the smallest luminosity?
        (1 pts) Which star has the highest surface temperature?
        (1 pts) Which star has the lowest surface temperature?
        (2 pts) Antares is a binary star. What is the spectral type of the more massive star? How do you know?

        (1 pts) Which of the spectral type B stars have finished fusing hydrogen in their cores?
        (1 pts) Among the main-sequence stars listed, which one is the most massive?
        (1 pts) Among the main-sequence stars listed, which one has the longest lifetime?
        (1 pts) Which star is the closest?
        (1 pts) Which star is the farthest?

      • (6 pts)In anger, you tell your best friend to "go jump into a black hole." You are pleasantly surprised when you find out she is actually going to do it. Describe what is seen from your perspective as she nears the event horizon. Then, describe what she experiences at those moments. Explain why there is a difference between these two perspectives.

      • (5 pts)The Crab nebula is what remains from a supernova that occurred in 1054 AD. Here are three images of the nebula taken at different wavelengths, adjusted so that each image is at roughly the same scale. Study these images (on-line is better) and answer the following questions:
        X-Ray Optical Radio
        1. Which type of radiation is revealing events with the highest energy?

        2. Which type of radiation represents events having the lowest energy?

        3. Based on what you read about the Crab [see the activity] and your knowledge of the different types of radiation, theorize on why the nebula is of such different angular sizes at the different wavelengths.

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