Welcome to http://www.handsonuniverse.org/activities/Explorations/PleiadesStars
Star Light! How Bright?
Explore the Magnitude Scale!
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 seems the brightest? ____________
Now let's measure the brightness of each star using Hands-On Universe software.
Open Pleiades.fts or . Next, flip the image horizontally, change the color palette, and center the image to include all the bright stars. (See following instructions.)
|Go to the Manipulation menu , select Flip, . Click on Horizontal, click OK.|
|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. (Purple works well.)|
|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 several stars' Brightness Counts at once with Find!
Or Measure each star's Brightness Counts with Auto aperture .
On the toolbar there is an icon which looks like bulls 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.
C. Record and Analyze.
Fill in the data table with the brightness counts for each star.
Pleiades Star Names
|For the rest of the star data, use the Auto Aperture tool instead of Find.|
D. Meet the Challenge!
How is the magnitude scale related to star brightness?
Compare the brightness counts of the stars to their magnitudes. Circle your choice.
What is the rule?
Think of yourself as a star astronomer!
Refer to the following and other references to find diagrams of the Pleiades or 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. (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 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.
Additional 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 in the South Building.
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 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.
Strand, K.A. Basic Astronomical Data.
HOU Educators: Pleiades .fts images
Assessment: Pleiades Stars Test Yourself
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