A Brief History of Science/The Role of Mathematics in Science Homework
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Galileo Galilei famously observed and drew the sun and its sunspots over the course of a summer. We still have the pictures he drew. If you would like to see his images strung together to make a movie, watch the video at the right. 

The images below are reproductions of two pictures Galileo drew: one on June 21, 1613, and the other on June 22, 1613. Let's assume the two drawings were made at the same time of the day, e.g., 8:00 a.m. C.S.T., and let's assume the diameter of the sun is known to be 1,380,000,000 meters.
The image below shows Galileo's drawing from June 21 superimposed on his drawing from June 22. The green line represents the distance traveled by the sunspot pair in twentyfour hours. Note: We know the sun is actually a sphere, and as a result, the surface of the sun is not flat. The images we are using are twodimensional and show the surface of the sun as being flat. Thus, by drawing the path of the sunspot pair as a straight line, we are introducing error into our measurement.
Now, stop for a minute and see if you can figure out how to use a ruler, the known diameter of the sun (given above), and the drawing above to calculate the distance traveled in twentyfour hours by the sunspot pair shown in the image above.
Calculating the Distance Traveled by the Sunspot Pair SelfQuiz
Gapfill exercise
Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!