Welcome to http://www.handsonuniverse.org/activities/Explorations/MoonMeasure/Slice&PixelScale

Use the slice tool to measure in pixels.

Use the calculator to find out the pixel scale. 

Measure a crater diameter using the slice tool.  Use image moon1.fts

1. Click on Data Tools. Select Slice.

2. Move the cursor to one side of the crater. Click on the mouse button and drag the cursor across the crater. Click again at the other side of the crater.  A red line will appear on the image.

3. A Slice window with a graph will pop up. If you need to move this window, click on the title bar (top edge) and drag the window to the side. When you click on the graph, a tiny box will move across your slice to indicate the position of the cursor with respect to the graph. The graph indicates pixel distance versus brightness counts.

4. To clear the image of your slices, click on View. Select Clean Up Marks. Or, click on the broom & dustpan icon.

5. Slice horizontally or vertically across the widest part of the crater. (This is especially important for craters near the "limbs" or outside edges of the apparent disc of the moon). Use the information in the pop up Slice window to determine the starting point and ending point of the crater diameter. Subtract to get the crater diameter in pixels.

Determine the pixel scale in kilometers on these moon images. (The pixel scale has to be calculated for each telescope and camera set up.  The scale you calculate here will be good for all of the moon images in Moon Measure.)

1. The crater Plato is 100 kilometers wide; this is the same as 62 miles. 

2. Measure Plato's diameter in pixels.   _____________

3. Open the calculator on your computer.   It is in the Apple menu on a Macintosh computer and in the Accessories Menu on a PC or IBM compatible computer.  

4. What is the pixel scale in kilometers? 
   Hint: Divide 100 kilometers by the number of pixels you measured for Plato's diameter.  
   Each pixel represents _________ kilometers. 

5. What is the pixel scale in miles? 
   Hint:  Divide 62 miles by the number of pixels you measured for Plato's diameter.  
   Each pixel represents _________ miles. 

6. To find the diameter of any crater, you will multiply the pixel scale (in kilometers or in miles) times the number of pixels in you measure on the image.  

7. Make a list or a table of the craters you measure, their diameters in pixels and their diameters in kilometers or miles or both!

01/09/2000

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