In this activity, students download NASA Hubble Space Telescope (HST) images of the Martian polar ice caps in summer and winter. Using image processing techniques, students measure and compare various images of the changing Martian and Earth polar ice caps.
depend on the lengths of the seasons. The fact the planet has a season depends on the tilt of the axis of rotation. The length of the season on each planet depends on the time it takes the planet to make one orbit around the sun.
Activity 1: Observe polar caps on Earth and Mars as they change over time. Sketch the ice coverage of Mars' polar caps at different times of the Martian year.
NASA scientists want to know, "How much does the polar ice cap on Mars change over time?" Let's use NASA Hubble Space Telescope images to find out.
Observe the diagram of Earth. Earth and Mars have similiar tilts of their axes of rotation.
View the on-line movie, Earth Changing Polar Ice Caps Animation several times.
View the on-line movie, Mars
Changing Polar Ice Caps Movie (mpg,
several times. In the space provided, carefully sketch: (i) the maximum
extent of ice coverage; (ii) the minimum extent of ice coverage; and (iii)
the average or middle extent of ice coverage.
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One procedure frequently used to conduct scientific investigations is called IMAGE PROCESSING. In this activity, students use technology to download and analyze images and movies of the dynamic Earth and Martian polar ice caps. Specifically, students will measure the areas of these polar caps and how they change over time.
Be sure you have the following items on your computer before you begin:
2. Open the image: Open the
winter image of Mars in TIF format by moving the pointer to the File pull-down
menu at the top of the screen, depress the mouse button, drag down to Open,
and let go. Select the HST image oct96_mars.tif.
You must use TIF format images with this image processing software,
but if you would like to see the image using a WWW-browser, it is oct96_mars.gif.
3. Set the Image Scale: Move the pointer to the Analyze pull-down menu at the top of the screen, depress the mouse button, drag down to Set Scale, and let go. A new window will open. In the center of the window is a box labeled Units. You must set the units first. Click on the down arrow in the box and select kilometers as your unit of measurement. At the top of the window enter 292 in the Measured Distance box and 4362 in the Known Distance box (this corresponds to a scale of 292 pixels = 4362 km). Click OK and start measuring!
4. Draw a Diameter: Using the Segment Tool (Tools window, 5th icon from the top in the right hand column, labeled "select lines"), draw the longest segment you can across the diameter of the white ice cap. Once the segment is drawn, return to the Analyze pull-down menu, drag down to Measure, and release the mouse button. Again, click on Analyze, drag down to Show Results, and release the mouse button. A Results window will appear with your answer in the column marked length. You may need to make the window larger.
5. Freehand Tool to Measure Perimeter and Area: This image processing program 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, to create 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 freehand any curve you want (this is called the Freehand Tool and looks like a heart). Determine the area of the polar ice cap using the freehand tool to trace the outside. Select Analyze and Show Results to view the measured value for perimeter and area. Record your results below.
6. How big is the winter Martian Polar Ice cap compared to the state or country in which you live?
7. Now that you know how to measure various aspects of Mars, let's get data for both the maximum and minimum extent of the Martian northern polar ice cap. The minimum extent image is mar97_mars.tif and available for viewing through your WWW-browser as mar97_mars.gif.
Record your data here:
Why or why not?
9. Does anything on Earth
compare to these sizes?
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Record your data below:
Click on the image to see the full size chart
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