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Pleaides Stars....

Brightness Counts and Magnitudes

Pleiades Puzzle: Star Light! How Bright?

This image of the Pleiades was taken in Oil City, Pennsylvania
on October 6, 1996, by the Oil Region Astronomical Society.

Background: All we know about stars is from star light! People have always noticed that some stars seem brighter than others. In the second century B.C., a Greek astronomer and mathematician named Hipparchus produced the first known catalog of star names and positions. He invented a scale with six categories to describe star brightness. He assigned each star a number value from 1 to 6 depending on how bright the star seemed to be in the sky. Star astronomers call these brightness categories, magnitudes.

Activity: Use Hands-On Universe image processing software and an image of the Pleiades Star Cluster to find brightness counts of the bright stars. Compare the brightness counts of the stars to their assigned magnitudes.

Challenge: Discover how astronomers arrange the magnitude scale to describe the brightness of stars!

Look at the stars of the Pleiades. Which star do you think is the brightest? ___________________________

 

A. Display the image of Pleiades for your analysis work.

Flip the image horizontally, change the color palette, and center the image to include all the bright stars.

  1. Go to the Manipulation menu, select Flip, click on Horizontal, click OK.
  2. Go to the box with the word GREY. Place your cursor over the arrow on the side. Click on mouse and drag to IGREY; click mouse again. Repeat the process to choose any color palette.
  3. Go to the side bars and arrows which frame the image. By clicking on the arrows, or by clicking and dragging on the side bars, you can change the portion of the image that you see. Position the image so the bright stars of Pleiades are in the image frame.

B. Compare Star Brightness ….. with Photometry (light measuring) Tools!

Either Measure the Starlight with Auto Aperture:

On the toolbar there is an icon which looks like bull’s eye. This tool is called Auto aperture. It gathers all the a starlight from a region, subtracts background ‘sky light’, and reports the number as brightness counts.

  1. Go to the toolbar, (second row at the top of the screen).
  2. Select Auto Aperture (the bull’s eye icon). Move the mouse over a star you wish to measure. Click.
  3. A brightness count number will appear next to the star! (A results box also appears. To remove the results box, click on File and select Hide window).
  4. To Clean up marks on your image, click on the icon which looks like a broom and dustpan.

Or Measure the Starlight with Find:

  1. Go to Data Tools. Select Find.
  2. Click on Threshold. Delete the number 4 in the center box. Type in 8000. Click OK.
  3. Brightness count numbers will appear next to the bright stars! (A results box also appears. To remove the results box, click on File and select Hide window).
  4. To Clean up marks on your image, click on the icon which looks like a broom and dustpan.

Record and Analyze:

Fill in the data table with the brightness counts for each star. List the stars in order of brightness counts.

Pleiades Star Names

Brightness Counts

(The numbers next to the stars.)

Magnitudes

(See Table of Magnitudes.)
     
     
     
     
     
     
     
     
     
     

C. Meet the Challenge! How is the magnitude scale related to star brightness?

  1. Which is the brightest star? _________________ What is this star’s magnitude? ________
  2. Which is the dimmest star? __________________ What is this star’s magnitude? ________

Compare the brightness counts of the stars to their magnitudes. Circle your choice.

  1. Stars with more brightness counts have a ( higher or lower ) magnitude.
  2. Stars with less brightness counts have a ( higher or lower ) magnitude.

What is the rule?

  1. In your own words, explain how the magnitude scale is arranged to describe the brightness of stars.

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Think of yourself as a star astronomer.

6. What other questions will you investigate about the Pleiades stars? About stars in general?

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Resources

Refer to the following and other references to find diagrams of the Pleiades.

Levy, David. Skywatching. A Nature Company Guide published by Time-Life Books. San Francisco: US Weldon Owen Inc., 1994. (1-800-227-1114).

Menzel, Donald H. and Jay M. Pasachoff. A Field Guide to the Stars and Planets, 2nd Edition. Boston, Houghton Mifflin Company, 1983.

Refer to the following and other references to read the mythology of the Pleiades.

Krupp, E.C. Beyond the Blue Horizon, Myths and Legends of the Sun, Moon, Stars and Planets. New York: Harper Collins Publ., 1991.

Stall, Julius D.W. The New Patterns in the Sky, Myths and Legends of the Stars. Blacksburg, Virginia: McDonald and Woodward Publ. Co., 1988.

Refer to the following and other references to read about the magnitude scale.

Levy, David. Skywatching. A Nature Company Guide published by Time-Life Books. San Francisco: US Weldon Owen Inc., 1994.

Menzel, Donald H. and Jay M. Pasachoff. A Field Guide to the Stars and Planets, 2nd Edition. Boston, Houghton Mifflin Company, 1983.

World Wide Web Pages for astronomy resources and education projects.

Star Hop to Pleiades Web Page….http://www.adler.uchicago.edu/ISE

Adler Planetarium and Astronomy Museum http://astro.adler.uchicago.edu

Hands-On UniverseÔ http://hou.lbl.gov

Bibliography and Credits

Briggs, John. Yerkes Observatory, Williams Bay, Wisconsin, University of Chicago. October 3, 1996 image of Pleiades (pleiades.fts) taken with a red filter on the 2 inch refractor, Bruce mounting.

Burnham, Robert Jr. Burnham's Celestial Handbook, An Observer's Guide to the Universe. Beyond the Solar System, Vol. III. New York: Dover Publications, Inc., 1978.

Cole, David. "Consultation Regarding Derivation Of R Magnitude Values." University of Chicago Astronomy Department. Oct., 1996.

Hands-On Universe Informal Science Education Project, Lawrence Berkeley National Laboratory, Berkeley, California.

Hirshfeld, Alan, Roger W. Sinnott, and Francois Ochsenbein. Sky Catalog 2000.0, Volume I: Stars to Magnitude 8.0, 2nd Edition. Cambridge, MA: Sky Publishing Corporation, 1991. pages 86-88.

Krupp, E.C. Beyond the Blue Horizon, Myths and Legends of the Sun, Moon, Stars and Planets. New York: Harper Collins Publ., 1991.

Levy, David. Skywatching. A Nature Company Guide published by Time-Life Books. San Francisco: US Weldon Owen Inc., 1994.

Menzel, Donald H. and Jay M. Pasachoff. A Field Guide to the Stars and Planets, 2nd Edition. Boston, Houghton Mifflin Company, 1983.

Stall, Julius D.W. The New Patterns in the Sky, Myths and Legends of the Stars. Blacksburg, Virginia: McDonald and Woodward Publ. Co., 1988.

Strand, K.A. Basic Astronomical Data.

The Pleiades: A Cluster of Stars in Our Galaxy!

In mythology, Atlas and Pleione are the father and mother of the Pleiades. The rest of the stars are the sisters!

Places to see the Pleiades at the Adler Planetarium!

First Floor "Night Visions" (tall gray kiosks near the cafe)

Night Visions Looking South

Night Visions Looking West

Landings on Stairs between the First and Second Floors

Historical Drawing of "Taurus" (north side stairs); look at the bull's shoulder for the small cluster of stars.

Photograph of the "Pleiades Star Cluster" (south side stairs)

"The Sun and Other Stars" on Third Floor (Near Milky Way Exhibit)

Look at the Pleiades Cluster on the upper curve of the display. Push the button next to Pleione. What is so special about this star? How is its color and size different from the Sun?

Sky Theater! (second portion of sky show)

Search for the Pleiades in the planetarium’s night sky!

Museum Store

…Poster #5… Star Finders… Cards.... Books… Etc.

 

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Hands-On Universe is funded by the National Science Foundation.

Version 110397 written by Vivian Hoette, Education Specialist, Adler Planetarium & Astronomy Museum for Hands-On Universe. vhoette@hou.lbl.gov