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Are Sunspots Really on the Sun?

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To do this activity, you first need to collect solar data.

Galileo's Dilemma | Your Experiment | Other Methods | More About Galileo

Galileo's Dilemma

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 appeared 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.

Galileo's arch-enemy Christoph Scheiner claimed the spots must be tiny undiscovered planets circling the Sun, which would occasionally pass in front of its disk. Galileo proved Scheiner wrong. How?

Your Experiment

To find out how Galileo proved Scheiner wrong, let's try an experiment.
  1. First, we're going to graph some of your sunspot data. Print out a copy of the Sunspot Speed Graph. Note that you will need to figure out the distance, in centimeters, "traveled" by the spot groups. You will graph that along with the groups' latitude.
  2. Pick your best sunspot group, the one for which you have the most data. What you want to find is how far that group appeared to travel across the Sun's disk.
  3. To figure out how far the group moved from the first to second day, subtract your measured distance (the one you measured on your sketch from the left edge of the Sun) of the first day from the measured distance of the second day. (e.g. if your Day #1 = 3 cm and Day #2 = 4.5 cm., the distance would be 4.5-3 = 1.5 cm). Now, graph that point above the latitude measurement for the second day.
  4. Figure out how far the spot group moved between each of the rest of your days, and place their points on the graph. If you have a day missing, figure the distance the spot group moved in 2 days and use half that amount for each of the 2 days.
  5. Once your data is plotted, draw a line/curve between the points. To minimize recording errors, graph one or two more sunspot groups just as you did the first.

What did you notice?

Did the spots' movement across the disk remain constant? If the distances traveled, and hence the speeds, were different, in what areas of the Sun did they appear faster, slower?

Other Methods

More About Galileo

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