Solar_rotation_Lab_01-09-10 - THE PERIOD OF ROTATION OF THE...

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THE PERIOD OF ROTATION OF THE SUN 1 1 Purpose: Use images of the sun to test the hypothesis that the sun undergoes differential rotation by calcuating the sun’s rotation rate using the motion of sunspots. Introduction: This is a lab designed to help you design and carry out a science investigation. You need to read through the entire lab before beginning and answer the preliminary quesitons on the answer sheet. Then you and a partner will come up with a plan to measure the rate of solar rotation using sunspot images. After measuring the rate of rotation for one set of spots you will be ready to test the hypothesis that the Sun’s rotation rate is different at different latitudes. Overall Strategy: The CLEA software associated with this exercise allows you to display images of the Sun from the GONG solar telescopes and to measure the positions of sunspots. The software details will be described later, but the basic idea of the scientific problem you will be investigating can be understood even before you get into the details of the software. Your primary goal is to use a series of the GONG images to figure out as precisely as possible how long it takes the Sun to rotate once, a number we call the sidereal rotation period of the Sun. Your value should be expressed as a number and a fraction of a day (e.g. 22.11 days). Since the images you have are spaced about 8 hours apart, you might think you could at least determine the rotation rate to the nearest 8 hours, or 0.33 day. The easiest way to determine the period of rotation of the Sun would be to find a sunspot and just watch it until it comes back to the same place on the images. But here are some questions you should ask yourself, and which you should try to answer when looking at the images. Record your answers on the answer sheet for this lab. 1. Which direction is the Sun rotating? Explain. 2. Do sunspots live long enough on the surface of the Sun to survive one rotation? Explain. 3. What if the rotation rate of the Sun isn’t evenly divisible by 8 hours (the average time between the GONG images in the database)? Will the spot return to exactly the same place on the images after one rotation of the Sun? 4. Think of several strategies that don’t require you to see a sunspot make one complete rotation which you can use to determine how long 1 Exercise developed from materials provided by CLEA (Computer Lab Exercises in Astronomy) at GettysburgCollege, Gettysburg, PA.
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it takes the Sun to rotate through a full 360 degrees? (Hint: What if you were only able to measure how long it takes to rotate through 30 degrees?) Calculating the Sidereal Period of Rotation of the Sun From your Measurements: The value you determine from Earth-based images of the Sun is what is called the synodic period of rotation. This is the apparent rotation period of the Sun as seen from the Earth, not the “true” rotation period of the Sun because the Earth is in motion, orbiting around the Sun from west to east as the Sun rotates. The “true” rotation period of
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This note was uploaded on 02/06/2011 for the course ASTR 114 taught by Professor Staff during the Spring '08 term at George Mason.

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Solar_rotation_Lab_01-09-10 - THE PERIOD OF ROTATION OF THE...

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