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Time that Period!


  1. Students will recognize a periodicity within a set of data.

  2. Students will learn how to complete and apply the method of Folding to finding the period of the periodicity.

  3. Students will apply the method of Folding to determine the periodicity of pendulums, sample data, and orbits of binary star systems.

  4. Students will learn an appreciation for basic astronomy and astrophysics through the exposure of such topics embedded in this lesson.

Grade Level

7th through 12th grades


This has been developed as a multi-day lesson plan. Each lesson day has been designed to take approximately an hour to complete. The lesson is broken down as follows:

    Prerequisites - Students review the concepts such as "Our Universe" or "Stars"

    Day 1 - Students complete a hands-on lab involving a pendulum and recognition of periodic behavior.

    Day 2 - Students apply the method of Folding to determine a period in sample data and from actual satellite data.

    Enrichment - Students learn and apply the chi-square test to determine the period in a set of data.


Students should know how to graph/plot data and determine the mean from a set of data. Students should have also been exposed to a variety of astronomy and astrophysical concepts, such as those discussed in the "Imagine the Science!" section of this Web site. Information in the Introduction section of this lesson's Day 2 can also be used.

Day 1

Day 2


  1. Kaufmann, William J. III, Universe, Freeman and Company, 1994, pgs. 336-435

  2. Kerrod, Robin, Encyclopedia of Science: The Heavens Stars, Galaxies, and the Solar System, Macmillan Publishing Company, 1991

  3. Kondo, Herbert, The New Book of Popular Science Vol. 1, Grolier Incorporated, 1982, pgs. 174-205

  4. Sanford, Peter W. and Salton, Jane and Laskarides, Paul, Galactic X-ray Sources, John Wiley and Sons, 1982 pgs. 161-162

  5. Seward, Frederick D. and Charles, Philip A., Exploring the X-ray Universe, Cambridge University Press, 1995

The graphics and other information found within this lesson can also be found on Imagine the Universe! which is located on the World Wide Web. The URL for this site is

Some of the data was retrieved within The HEASARC Data Archive using W3Browse which is located on the World Wide Web. The URL for this site is

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

The Imagine Team
Acting Project Leader: Dr. Barbara Mattson
All material on this site has been created and updated between 1997-2012.

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