In this lesson, students will analyze data from solar magnetogram images collected over 25 years at the National Solar Observatory Vacuum Telescope at Kitt Peak, AZ. Students measure the solar diameter for each available day of a fifteen or sixteen month period of time of their choosing. This data can be graphed using spreadsheet and graphing software to illustrate the change in the sun's apparent diameter as measured from Earth.

Students will notice that the data collected is "noisy", i.e. that there is considerable random variation of the measurements from day to day, but the overall pattern of apparent size variation can be seen from the graph they construct.

Save time by sampling 2-4 images per month. Sampling each day in the sixteen month period improves the final plot. Have students work in groups of 2 or 3 to speed up the process.

You should be able to answer the following when you have completed this exercise:

1. Determine the date of aphelion, or maximum Sun-Earth distance, in Earth's orbit from your graph.
2. Determine the date of perihelion, or minimum Sun-Earth distance, in Earth's orbit from your graph.
3. Compare graphs from several years, does the approximate date of aphelion and perihelion occur at the same time through these years?
4. What is the maximum and minimum diameter of the solar images in pixels?
5. If the scale of these images is 4.6 arc-seconds per pixel, what is the maximum and minimum diameter of the solar images in arc-seconds? In kilometers?

Navigate to the disk drive that contains the DASL disk.

A list of options similar to those you see to the left will appear.

Choose Magnetograms and open that folder.

Inside the Magnetograms folder are data folders with images from the years 1977 through 2002.

Choose a year by double clicking on the folder, or single clicking on it and choosing Open.

Inside each folder are magnetogram images for each date for which an image was taken. The file names indicate the year, month and date in the following format:

900101MA is the magnetogram png file for January 1, 1990.

Open the image by double clicking on the file name.

The image to the left shows the magnetogram image for January 1, 1990.

To measure the diameter of this image, choose Plugins from the menu bar and Macros from the drop down box.

Choose "Log Date and Diameter" from the drop down box.

Quick Key Tip: You can also use the F5 key on your keyboard to activate this macro.

A Log Results window similar to the one to the left will open. It will show the Date and Diameter for the image that is currently opened on the screen.

Choose OK.

A Results table will open with the date and diameter data from the Log Results window.

Quick Key Tip: You can also use the letter O key on your keyboard to view the files and select your next image.

Open the next image for the year and continue logging date and diameter information.

Note: depending on your computer's memory, you may be able to open several days or weeks of images before closing them. If memory is an issue, close each image before opening another image. All data collected will be stored in the Results table.

When you have collected data for two or three months of dates, you should probably save your results table. To do this, choose Edit from the menu bar of the Results Table window. Choose Save As from the drop down menu. Navigate to a directory or disk drive where you can save your data and give your table an appropriate name. The generic name "Results" will appear in the file name bar. Change it to a more descriptive name such as "Diameter results 1990".

To graph the data from your results table, choose Edit from the menu bar and Copy All from the drop down menu that opens. This will copy the date and diameter information to the clipboard. Paste the data into a spreadsheet program and generate a graph. The image below shows a sample graph that was prepared with data collected for the images from October 1989 through April 1991. A 4th order polynomial trend line was added.