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portrait of Galileo Are Those Sunspots Really on the Sun?
See the Activity in Action Summary of Activity:
Students will acquire solar images (or draw sunspots), and record coordinates of sunspots. They will calculate and plot their apparent movement and describe their shapes. They will determine whether sunspots are features on the surface of the Sun, or objects in orbit around it.

(To see the printable version of this activity, click here)


Duration of Activity:

About 1 hour for preparation, 1/4 hour per day for 10-14 days if you choose to collect new data; at least 1-3 hours for analyzing data, answering questions and doing optional calculations.

Student Prerequisites:

  1. Basic knowledge of the Sun and planets.
  2. Concept of coordinates, longitude and latitude.
  3. Measuring, plotting, basic geometric terms, i.e. "width-to-height ratio".
  4. Optional - angular velocity (speed of rotation), vs. linear velocity, high school mathematics.
Preparation & Supplies Needed:
  1. Sunspot Recording Worksheets.
    Print out and make enough copies for each day of your observations.

  2. Latitude/longitude grids. (You may have to enlarge/shrink these with your computer or copier to make them match your solar disk images. And it will be easiest if you can copy them onto transparency paper.)

  3. Sunspot speed graphs. Print these out or make copies for each person.

  4. Computer & access to the internet. You will download an image of the Sun every day, for about 2 weeks (either intensitygrams or magnetograms).

  5. Copier machine and transparency paper (recommended)

  6. A basketball and a tennis ball (optional)

When Galileo Galilei discovered sunspots, he had a problem. Here it was, 1612, and he had just pointed his new version of the Dutch tool called a "telescope" towards the heavens. Not only did he discover the moons of Jupiter, the "seas" and craters on our own Moon, and the phases of Venus, but he also found what he thought to be dark smudges on the Sun. How could this be? After all, the Catholic Church taught that the heavens were perfect. So there could not be imperfections, or spots, on the Sun. (Remember that it is dangerous to look directly at the Sun through binoculars or in any other way!)

The German astronomer Christoph Scheiner claimed the spots must be tiny undiscovered planets circling the Sun, which would occasionally pass in front of its disk. Try this experiment and see if Galileo was right!

  1. Objectives:

    Students will:
    1. Observe sunspots and consider ways to determine whether they are on the Sun, or in orbit around the Sun (Galileo's dilemma).
    2. Collect and record sunspot data (images) for 2 weeks, or use sample data provided.
    3. Tabulate data and draw inferences from their numbers.
    4. Answer questions, and participate in group discussion, before the activity and after.

    Grade Level:
    5 - 12

  2. Procedure

    Please read the whole procedure, and complete the quiz and group discussion before you begin collecting data. Note that most (but not all!) sunspots appear in groups, so to make things simpler we will call them sunspot groups, even in cases when there may be just one sunspot.

  3. Data Analysis

  4. Questions
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