# Physics

• ## Module 04 – Measuring and Classifying Stars

The Hertzsprung-Russell diagram is an important tool in the classification of stars and the understanding stellar evolution. The H-R diagram was discovered independently by two astronomers in early 20th century using observations of star luminosity and surface temperature. With this lab exercise, you will use Stellarium to collect stellar information and then form your own H-R diagram and see if you can find how stars are group into different luminosity classes.

Background Question – Describe the four major groups of stars and where they are located on the H-R diagram.

Object: Explain the purpose of this laboratory assignment in your own words. What do you think you will accomplish or learn from this exercise?

Hypothesis: Write a simple hypothesis connected to different stars and the H-R diagram that you will be able to test up the Stellarium software (for example, most bright stars visible in the night are supergiants)

Procedure:

• Open the Stellarium software. Open the Sky and Viewing options window (F4). Under the “Sky” tab, uncheck the Atmosphere and Dynamic eye adaption.
• Select the Landscape tab and uncheck “Show ground”.
• For this lab, you will need to record the spectral class and absolute magnitude of a group of near stars and a group of the brightest stars in the night sky. For each star, open the Search window (F3) and enter the star’s name. Click on the star and look at the displayed information at the upper right. Record the star’s spectral class and absolute magnitude in the chart. Some information has already been include in the chart.
• Repeat step 3 for each of the stars on the list.
• Plot each of your stars on the H-R diagram below. Denote each star by their listed star number and mark the nearest in red and the brightest stars in blue.
• Using the H-R diagrams in Chapter 12 as a reference, mark out where the main sequence line, giant branch, supergiants branch, and white dwarfs region would be on your H-R diagram.

Q1: Based on the location of the Sun on your H-R diagram, what luminosity group (main sequence, giant, supergiant, or white dwarf) does the Sun belong to?

Q2: What stars did you find to be supergiants?

Q3: What luminosity group and spectral classes are most nearby stars?

Q4: What luminosity groups and spectral classes do most of the bright stars belong to?

Q5: Is there any part of the H-R diagram that you do not find any stars?

• Continue using Stellarium if you need further information to test your individual hypothesis. If you need further direction, please ask your instructor.

Conclusion: In 1-2 paragraphs, explain if your observations and data support or conflict with your hypothesis and if you have met your assignment objective. Was there any portion of the assignment that was particularly interesting or difficult?

 Brightest Stars in the Night Sky # Star Spectral Class Absolute Magnitude 1 Sirius A 2 Canopus 3 Alpha Centauri A 4 Arcturus 5 Vega 6 Capella A 7 Rigel 8 Procyon A 9 Betelgeuse 10 Hadar 11 Altair 12 Aldebaran 13 Spica 14 Antares A Nearest Stars # Star Spectral Class Absolute Magnitude 1 Sun G2 4.8 2 Proxima Centauri M6 15.6 3 Alpha Centauri A 4 Alpha Centauri B K1 5.7 5 Barnard’s Star M4 13.2 6 Wolf 359 M6 16.7 7 Lalande 21185 M2 10.5 8 Sirius A 9 Sirius B wd use B1 11.2 10 Epsilon Eri 11 61 Cyg A 12 61 Cyg B 13 Procyon A 14 Procyon B wd use A6 13

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