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Measurement of Crater Shadows

Measurement of Crater Shadows

Using XVista and your copy of the moon image, measure the lengths of the crater shadows for the two largest craters on your image. Your measurement should be in units of pixels. Do this as follows:

  1. Display the enhanced image using the TV command.
  2. Zoom in on the crater of interest.
  3. Place the cursor at the center of the crater and measure the location of the center in (x,y) coordinates on the image.
  4. Measure the length of the crater shadow by locating the (x,y) image coordinates of the leading and trailing edge of the shadow with the cursor. Denote the location of the leading edge as (xl,yl) and the trailing edge as (xt,yt). The length of the shadow, s will just be the geometric distance between the two:Make an estimate the uncertainties in your measurements, giving what assumptions you have made (think about what fraction of a pixel you can make measurements of the positions of features)..
  5. Also measure the apparent diameters of the craters in a similar way.
  6. Using the tabulated true distance of the moon (from The Astronomical Almanac as found above), and remembering that this is the distance between the centers of the Earth and Moon (and that we and the lunar features we are observing are on the respective surfaces), estimate the number of kilometers per arcsecond in our lunar images (i.e., how many km does 1 arcsecond correspond to).
  7. Make a table of your measurements, giving the following:
    1. The pixel coordinates on your images of the crater centers
    2. The lengths of the crater edge shadows in pixels, arcseconds, and km.
    3. The apparent diameters of the craters in pixels, arcseconds, and km.
    Remember to include your estimates of the uncertainties of these measurement