Background:
Ancient peoples used to think that the surface of our Sun was perfectly smooth and had no spots. Now that we have satellites and telescopes, dark spots can be observed on the Sun’s surface. These spots appear dark to the eye because they are cooler than the surrounding gas although they are still quite hot! The photosphere has a temperature of about 5500 degrees Celsius and a typical sunspot has a temperature about 3900 degrees Celsius. Sunspots have two components - a dark inner penumbra and a lighter outer umbra. A sunspot's lifetime can be as short as an hour or two or as long as several months. The number of sunspots that can be seen on the surface of the Sun increases and decreases in a regular pattern, known as the solar cycle, with a maximum number of sunspots occurring every 11 years.

Have students predict the size of a sunspot. Is it as big as their residence? an apartment complex? the moon? the Earth?

Procedure:
Part I - Downloading, saving, and converting images from the Internet

Any image that you find on the Internet's World-Wide-Web (WWW) using Netscape or MS Internet Explorer can be saved on your hard drive or in a folder on your desktop for analysis. It might be helpful to create a new folder on your desktop and label it “IMAGES OF SUNSPOTS”. Then you can OPEN this folder and save all your images to it.

1.Start your WWW browser (Netscape or MS Internet Explorer, for example) and enter in a URL that has lots of images. The following site is the one I used to download lots of sunspot images: http://www.sunspot.noao.edu/ftp/esf_shg/

2.To save an image to your hard drive or desktop folder, position the mouse over the image and hold down the button for a couple of seconds (use the right button if you have more than one button on your mouse).

3.A menu will appear and you can select SAVE THIS IMAGE AS. This will give you an option about what to call the image and where to save it. If you’ve created a folder on the desktop in which to save your images, be sure this folder is open when you save the sunspot image. Choose a different name and location if you like.

4.The image is now saved and you can open it with your WWW browser or with an image conversion program. With these programs, you can alter the image's size, color, or even add text to the image.

5.Most images on the Internet are in GIF or JPG. Image processing software do not typically use files in this format so they must be converted to TIFF format.



6.Start your graphics conversion program by double clicking on its icon. From the FILE menu, select OPEN. Find the image that you downloaded and open it using this converter program.

7.From the file menu, select SAVE AS. Click and hold on the format box. A pop-up menu will appear. Select "TIFF". Then click SAVE. Close your graphics converter program. You are now ready to begin image processing.

Part II - Using Image Processing Software for Scaling and Measurement

		1.Start your image processing software program. Using the FILE pull-down menu, select OPEN. Select the TIFF image that you converted in Part I. 2.The first task is to calibrate the image (tell the computer the scale of the image). If you are looking at an image of Sun you must know its diameter which is approximately 1.4 million km {or 1.4e6 km). Using the segment tool/select line tool (fifth from the top on the right), draw a line across the diameter of the Sun. 3.Under the ANALYZE menu, select SET SCALE. Note that the computer has already recorded how many pixels (picture elements) long the line you drew. First, change the UNITS to KILOMETERS. Second, enter in the known diameter, 1.4e6. Click OK. Your image is now calibrated and you are ready to measure sunspots!! 4.Click on the magnifying glass in the upper left of the tool bar. Use it to focus on one of the sunspots by clicking on it. The software will remember the scale of the image so you can get as close as you need to make a good measurement. To un-zoom, double click the magnifying icon in the tool box. 5.Use the segment tool (select lines) to carefully draw a diameter across the entire sunspot. From the ANALYZE menu, select MEASURE. 6.From the ANALYZE menu, select SHOW RESULTS. You might have to grab the bottom left hand corner of the new window to expand the window to see your results.( Note: If you’re using NIH Image to process your image, the window in the lower left corner of your computer screen will have the results of your measurements.)

7.Determine the diameter for several sunspots. How big are they? Are they bigger than your house? Are they bigger than Earth?

8.You can use the same Segment Line Tool to Measure Perimeter and Area. This image processing program, NIH Image, has 4 tools for selecting regions for study. The first tool in the right hand column of the tool window is used to drag out rectangular areas. The second tool in the right hand column of the tool window is used to define oval or circular areas. Using the third tool in the right hand column of the tool window, you can connect a sequence of points with line segments, creating a polygon of your own design. To close the polygon (connect your last point to your first point), just click the mouse twice in rapid succession. The fourth selection in the right hand column of the tool window allows you to draw freehand.

10.Determine the area of a sunspot using the freehand (heart-shaped) tool to trace the outside. Select MEASURE from the ANALYZE menu, then select SHOW RESULTS from the ANALYZE menu to view the measured value for perimeter and area.



Coding:

Maryland Core Learning Goals (Science): Expectation 7; 7:3
National Standards (Science): A 3; A 8; E 2
National Standards (Geography): Standard 1; 8:2
National Standards (Mathematics): Standards 4:4; 13:1; 13:5

The following site is a sampling list of sunspot images:

http://www.sunspot.noao.edu/ftp/esf_shg/

You can assign each of the images to pairs or groups of students to give them practice in using NIH Image to calibrate and measure sunspot images. Have students keep track of the image they were assigned, the diameters of each sunspot they measured, the area of their sunspot, and about how many Earths would fit across the diameter of their sunspot. Earth’s diameter is 12,800 km.



Credits:
Linda McClelland
IMAGE/POETRY http://image.gsfc.nasa.gov/poetry