The Sunspot Cycle

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Clemson University *

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1040

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Physics

Date

Dec 6, 2023

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docx

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The Sunspot Cycle These lab activities have evolved over years of use in Clemson University’s Department of Physics and Astronomy general astronomy laboratory. Contributors include Tom Collins, Mark Leising, Neil Miller, Peter Milne, Grant Williams, Donna Mullenax, Jessica Crist, Keith Davis, Amber Porter, Lea Marcotulli, and David Connick. Please direct all questions, complaints, and corrections to David Connick (dconnic@clemson.edu) who is responsible for all errors and omissions. I. Introduction In AD 1609 the Italian astronomer Galileo Galilei was the first European known to observe sunspots. Galileo discovered that these spots moved across the disc of the Sun from day to day. This seemed to be conclusive proof that the Sun rotates! To observers, and in photographs, sunspots look dark. The temperature of the photosphere of the Sun is on the order of 6000 K (about 10,300 o F) while sunspots are at about 4000 K (about 6700 o F). Thus sunspots look dark by contrast to the much hotter (and therefore brighter) background of the photosphere. Sunspots are essentially the result of magnetic storms on the Sun's photosphere. Aurorae on Earth are associated with the number and intensity of sunspots and, indeed, one of the most obvious properties of sunspots is their cyclic character and their association with auroral activity on Earth. The number of sunspots and the locations of those spots seem to have a periodicity of about 11.1 years. If the polarity of the magnetic fields in the spots is included in determining the cyclic period, it is about 22.2 years. There is some evidence that weather cycles on Earth are linked to this longer sunspot cycle as you will see below. In order to document the behavior of sunspots, a continuous check on the numbers of spots is maintained by solar astronomers. Groups of spots are often very complicated and a count of the number of spots can be somewhat subjective. To reduce the variation introduced when different astronomers count the spots, the Wolf number system gives a lone spot a value of one and a group of spots a value of 10. This weighs the Wolf number in favor of groups and tends to reduce the subjectivity of the count. (There are additional safeguards in the counting system. They are not important to this discussion.) II. Sunspot Observations Open the Starry Night file “Sunspots.skyset”, you should see the sun and a group of sunspots near the center. Double check that the time step is set to 1 day. Using the time step watch the sunspot group move each day and answer questions 1-3 on the worksheet. Next we will look at some images of sunspots. Open the “Sunspot Images” file which should contain 4 images and descriptions below each image. Use these images and the descriptions to answer questions 4-16 on the worksheet.

III. Plotting Sunspot Data Now we will use real sunspot data to create plots and analyze the sunspot cycle. Open the “Sunspot Number Data” file where you should see a table of years and sunspots in that year. Your goal is to make a scatter plot of the data. 1) Highlight the entire set of data. 2) Go to ‘Insert’ then ‘chart’ , a line plot will appear. 3) In the chart editor on the right side of the screen make sure the type is line chart. 4) Go to the customize tab in the chart editor and open the horizontal axis options. 5) Set the minimum value to 1745 and maximum to 1975 6) Go to ‘gridlines and ticks’ in the chart editor. 7) Set the horizontal axis major spacing to ‘step 20’ and the minor spacing to ‘step 5’. 8) Go to chart and axis titles, to change the title to “(your last name) sunspots by year” 9) Make any other adjustments to the style of your plot that you wish. When your plot is complete, copy it to your worksheet, fill in the table and answer questions 17- 19 on the worksheet. Now we will look at the latitude of the sunspots during the cycle. Open the data set “Sunspot Latitude Data”. We want to plot the North latitude data on the same plot as the South latitude data so you will need to change the South latitude numbers to negative values. Plot requirements. 1) Scatter plot chart type 2) No legend 3) Vertical axis labeled “Latitude” 4) Horizontal axis labeled “Year” 5) Title: “(your last name) Sunspot Latitude by Year” 6) Colors and other style options are up to you. Once your plot is complete, copy it into your worksheet and answer questions 20-22 on the worksheet. For questions 23 and 24 on the worksheet use a web search to determine your answer and be sure to cite your sources.

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