Lesson: Measuring the Motion of a CME Using NIH Image

(Grades 9-12)

Teacher information

These are instructions for measuring the velocity and acceleration of a CME using NIH Image software. Read the Motion of a CME Lesson Plan first.

Further Objectives:

  1. To demonstrate the ability to use image software from the net.
  2. To demonstrate the capability of moving data from one program to another.



A. Bringing Down An Image

  1. Go to the CME LASCO image on the SOHO pages at
  2. Click and hold on the first image. A window will open. Move the cursor to Save this image as... and release. Save this image in a place on your computer that you will be able to access easily. It would also be a good idea to name the image just in case you will need to search for it.

B. The Activity

Make sure that you have NIH Image in your computer as well as a spreadsheet program. If you are working with students, it would be a good idea to have a program such as Lotus 1-2-3 or ClarisWorks that will allow the students to print reports using different programs. These programs have spreadsheets as well as word processing programs that will allow easy transfer from one type to another.
  1. Open NIH Image.
  2. Go to the ANALYZE menu and pull down to OPTIONS. You will get this screen.
  3. Use NIH image to calculate the scale of the image:
    a. Click the boxes for AREA and PERIMETER/LENGTH. Click OK.
    b. Using FILE from the pull-down menu, select OPEN.
    c. Open the first LASCO image of the CME that you down-loaded from the SOHO web-site. (NOTE: The image must be in PICT or GIF format. This may mean opening the image with a translator program and then saving it under one of these formats)
    d. Note that at the bottom of the image there are white tick marks. These marks show the diameter of the Sun. It is possible to print this image and do the work by hand. Select the measuring tool and starting from the center of one white tick mark click and drag to the center of the next tick mark. (if you hold the shift key down it will automatically draw a straight line)
    e. Go to ANALYZE and then to SET SCALE. The following window will open:
    f. The measured distance is in pixels as seen by the units. If you click on PIXELS next to UNITS you can choose the units you wish. We would suggest that you choose kilometers.
    g. In the KNOWN DISTANCE box (that should be highlighted) type in the diameter of the Sun in kilometers. This distance is 1,392.000.
    Click OK.
  4. Measure the location and area of the CME
    a. Move the cursor (measuring tool) to the edge of the occulted area and draw a line to the edge of the CME.
    b. Go to ANALYZE then MEASURE. When you release the mouse on MEASURE it will automatically measure and scale the distance along that line. It will also measure the area of the line. This can be adjusted later.
    c. Next go to OPTIONS then THRESHOLD. The color of the screen will change and the LUT (Look Up Table on the side) will change to black and white. Your cursor will also change to a "+". By moving the black bar along the LUT you can change the color of the pixels to black. You will notice that at one point the CME will be white while all of the background will be black.
    d. Chose the wand tool (it looks just like a magic wand) and click along the outside edge of the CME until "dancing ants" surround the gas ball.
    e. Go to ANALYZE then MEASURE.
    f. Open the next image and redo steps 10 through 14.
    g. Once all of the images have been processed, go to ANALYZE then SHOW RESULTS.
    When you go to ANALYZE and SHOW RESULTS you will see a screen like the one to the right.
    The first number is the area of the line and the second is the distance along the line. Remember that the first measurement you took was the length of the line and the second was the area of the expanding gas. We therefore do not need the first area and the second length. As stated before, we will change this later. Note that your numbers will not be the same as above.
    h. Go to FILE then SAVE AS. Select MEASUREMENT from the buttons and save.
  5. Transfer data to a spreadsheet program
    a. Open the above file with a word processing program. Go to EDIT then COPY MEASUREMENTS.
    b. Open your spreadsheet program and paste the results of the
    measurements. This is where you will have to delete the measurements that you don't need. (see step 16).
    c. Using the instructions for your spreadsheet program, make a table that will show velocity and acceleration of the CME away from the Sun as well as the change in the area of the CME.

Return to the Motion of a CME Lesson

Created by: Dennis Christopher
Direct Comments to: dennis.christopher@gsfc.nasa.gov

Last modification: Friday, 09-Nov-2007 11:33:35 EST