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Galileo's Battle for the Heavens

Classroom Activity

To construct and evaluate graphs of the current sunspot cycle.

Materials for each student
  • copy of the "Plotting the Spots" student handout (PDF or HTML)
  • 5- or 10-square-per-inch graph paper
  • pencil
  1. Galileo studied sunspots, sketching pictures of the changing pattern of spots on the Sun over time. In this activity, students will study the nature of sunspot cycles.

  2. Lead a class discussion about sunspots. (See Activity Answer for detailed information on sunspots.)

  3. Following the discussion, give each student a copy of the "Plotting the Spots" student handout.

  4. Review with students the definitions for solar minimum and solar maximum. Have them study the sunspot cycles from 1900 to 1995 on the graph found on the student handout. Ask students to look for patterns in the data.

  5. Have students label the graph with an x for each solar maximum and an m for each solar minimum. Have them estimate the year when each cycle started and when it ended, calculate the length of each cycle, and calculate the average length for the nine cycles shown on the graph. Discuss their results. Be flexible with the accuracy of reading the years of solar maximum and minimum. The average should be approximately 11 years.

  6. Provide students with graph paper. Have them graph the data for Solar Cycle 23. If using 5-quadrille paper, students will each require three sheets; if using 10-quadrille, students will require two sheets.

  7. When students' graphs are complete, discuss their results using the questions on the student handout. You might want to make an overhead copy of the graphs to facilitate the discussion.

  8. As an extension, have students research whether the year 2000 solar sunspot maximum caused any significant disruptions in communications on Earth. Were any abnormal auroras reported? Were any satellites, Earth-bound communications, or power systems influenced by the solar maximum? For more information, see:

Activity Answer

Historical records show that sunspots may have been observed as dark spots on the Sun at least 2,000 years ago. Ancient people might have seen these dark spots when the Sun was low on the horizon and partially obscured by clouds or mist, since it would have been impossible to look directly at the bright Sun without damaging the eyes. It was not until about 1610, following the invention of the telescope, that Galileo and others began observing and writing about the dark spots they observed.

Sunspots are cooler areas on the Sun that appear as dark spots. While most of the visible surface of the Sun has a temperature of about 5700K, sunspots are only about 4,000K. Though they vary in size, most are larger in size than the diameter of Earth. Scientists say sunspots would be expected to glow orange in the sky, many times brighter than the full Moon, if pulled away from the Sun. They theorize that the spots are the result of magnetic Želds. The number of sunspots is cyclical, with periods of many sunspots (solar maximum) and periods of fewer sunspots (solar minimum). Solar flares, or explosions on the Sun, often occur near sunspots.

Students will notice the cyclical nature of the sunspot cycle. Each cycle is similar in shape and lasts about the same amount of time. The number of sunspots observed at solar maximum varies, however, from a maximum of nearly 200 sunspots to a low of about 60 (sunspot numbers are averaged monthly).

Students will have to estimate from the graph exactly the year and month. The average will be approximately 11 years.

Graph of Solar Cycle 23

Solar Cycle 23 began about mid-1996, and reached solar minimum about October 1996. Solar maximum occurred about mid-2000. The next solar minimum is predicted to occur sometime about 2006 and peak sometime about 2010. Predictions are based on approximate 11-year cycles with solar maximum occurring on average a bit less than halfway through each cycle.

Links and Books


Drake, Stillman. Galileo: A Very Short Introduction. New York: Oxford University Press, 2001.
Presents a short introduction to Galileo's life and achievements focusing on his conflicts with theologians but supporting the hypothesis that he was a zealot for, rather than against, the Catholic Church.

MacLachlan, James. Galileo Galilei: First Physicist. New York: Oxford University Press, 1997.
Contains a detailed chronology of Galileo's life and sidebars explaining his scientific contributions.

Reston, James, Jr. Galileo: A Life. New York: HarperCollins Publishers, 1994.
Chronicles the rise and fall of Galileo, focusing on his political instincts, his intellectual self-assurance, and his trials with the Catholic Church.

Sobel, Dava. Galileo's Daughter: A Historical Memoir of Science, Faith, and Love. New York: Walker and Company, 1999.
Presents a human picture of Galileo the scientist and Galileo the father.

Web Sites

NOVA Online—Galileo's Battle for the Heavens
Learn all about Galileo, from his place in science to his mistaken belief that Earth's daily rotation and its annual orbit around the Sun triggered ocean tides. Includes online activities.

The Galileo Project of Rice University
Contains an illustrated biography of Galileo, translations of letters from his daughter, information about other scientists of his time, a portrait gallery, and links to other resources.


The "Plotting the Spots" activity aligns with the following National Science Education Standards and Principles and Standards for School Mathematics:

Grades 5-8

Earth and Space Science

Science Standard D:
Earth and Space Science

Earth in the solar system

  • The Earth is the third planet from the Sun in a system that includes the Moon, the Sun, eight other planets and their moons, and smaller objects, such as asteroids and comets. The Sun, an average star, is the central and largest part in the solar system.

Math: Probability

Mathematics Standard 11:
Data Analysis and Probability

Grades 9-12

Earth and Space Science

Science Standard D:
Earth and Space Science

Energy in the earth system

  • Earth systems have internal and external sources of energy, both of which create heat. The Sun is the major external source of energy. Two primary sources of internal energy are the decay of radioactive isotopes and the gravitational energy from the Earth's original formation.

Math: Probability

Mathematics Standard 11:
Data Analysis and Probability

Teacher's Guide
Galileo's Battle for the Heavens

Video is not required for this activity