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Sun Spot Analysis

Activity and Starting Point page by R.M. MacKay. Clark College, Physics and Meteorology.

This material is replicated on a number of sites as part of the SERC Pedagogic Service Project


Introductory students use Excel to graph monthly mean Greenwich sunspot numbers from 1749 to 2004 and perform a spectral analysis of the data using the free software program "Spectra". Short answer and thought questions related to the graphical data are asked throughout the assignment.

Used this activity? Share your experiences and modifications

Learning Goals

  • Learn about the past sunspot record.
  • Graph monthly mean Greenwich sunspot numbers from 1749 to 2004.
  • Read the graph and answer questions related to the graphical data.
  • Learn how to download and install the Spectra software program
  • Perform a Fourier analysis on the monthly mean sunspot record using the Spectra Program.
  • Learn about Fourier frequency analysis
  • Use the relation between frequency and period of a component of the signal.

Context for Use

This activity is useful in any introductory geoscience course in which a discussion of the solar cycle is appropriate or in which an introductory exposure to Fourier spectral analysis is desired.

Teaching Materials

The assignment in a form that can be printed and handed out to students is:

Teaching Notes and Tips

  • The activity takes approximately 3 hours to complete. Omitting the last part on spectral analysis would likely make it a 2-hour activity.
  • Little background mathematics is required for this activity.
  • Students should be familiar with using Excel to make an X-Y graph and with the concept of period and frequency of a sinusoidal signal.
  • For students needing a refresher on using Excel Graphing with Excel (more info) can help refresh them.
  • More information on related to using Excel and related links can be found at How to use Excel

The two graphs above show essentially the same thing. The graph on the right was made with Excel by importing the Text frequency data from the Text output Window of Spectra. The Spectra program does not allow you to alter the horizontal axis. We did not ask students to do this step in the assignment since they can read the numerical values from the graph or from the table, but you may want to use these two figures in a follow-up discussion.


The successful completion of this activity and evaluation of their results are good measures of student comprehension. Follow-up discussions in class, essay questions on exams, and the future success of students on other related activities are also useful measures of student understanding.

References and Resources