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This lab is based on an unfiltered CCD image of craters near the center of the first-quarter moon that were acquired with a SpectraSource Instruments Teleris CCD camera on the old 12-inch Tinsley telescope that used to reside in the dome on the roof of Smith Lab. The images were taken on 1998 September 28 EDT.

The Teleris camera uses a Kodak KAF-0400 768×512 CCD with 9-micron pixels. The Tinsley reflector was a 12-inch (0.305-meter) aperture telescope with an f/16 cassegrain focus. The CCD was roughly aligned with its long axis oriented along the East-West direction in the sky, and the short axis North-South. Both zero (bias) and flat-field calibration images were also acquired. Because the integration times are so short, no dark images were required.

Because we are viewing these craters just after dawn from their point of view, the crater walls cast long shadows. Using a simple geometric technique pioneered by Galileo Galilei in 1610, we can estimate the physical heights of the crater walls. Along the way we’ll learn some basic image processing techniques.


The goals of this lab are as follows:

  1. Learn to read in and display the image using the XVista package, and to make measurements of the apparent sizes of objects.
  2. Learn how to identify a field using a finder chart (in this case, a photographic lunar atlas to identify the features in our CCD image), and to compile additional data (selenographic coordinates, and sun-earth-moon position information) from available catalogs (both books and online).
  3. Using simple geometry, estimate the heights of crater walls from the lengths of their shadows, with uncertainty estimates, and compare these to typical measurements as available.

This lab will make use of the Linux workstations in MP4042 and the XVista image processing package. You will also need to use an Internet browser to search some online catalogs for information (either your own PC or one of the Windows PCs in MP4042), and you will need to use the reading room to consult copies of the various Lunar Atlases and The Astronomical Almanac for 1998.


Part 1: Examine the CCD Images using XVista

Login to one of the Linux workstations in MP4042. For this guide, I will denote Unix commands by a “%”, which is the generic Unix command prompt. Commands in this guide given without a % are XVistacommands (i.e., issued in response to the XVista “GO” prompt).

For this part, do the following:

  1. Copy the raw data for this lab into your working directory by typing % cp /home/regulus/ast350/LabData/MoonLab/moon98.fits . If you type this command again, it will replace your working copies with new copies (and wipe out the old ones). It copies one (1) files into your working directory: moon98.fits, a pre-processed FITS-format image of the moon described above.
  2. Startup the XVista program in an xterm window by typing % xvista once you get the XVista command prompt (GO:), you are ready to begin. For details on basic XVista commands, see the Vista Tutorial and Cookbook in the white binder in the lab workstation area.
  3. Read in moon98.fits and display it. You may need to adjust the brightness and contrast using the L= and Z= keywords of the TV command. Adjusting the display contrast this way is far better than messing with the color bar at the bottom of the display (and less misleading). You can estimate the data values in the image by using the cursor and moving it over the image and noting the display of (x,y) position and “Intensity” in the box at the lower left-hand corner of the XVista TV Display window. This will help you chose sensible values of the zero-point ans span (Z and L, respectively).
  4. Practice zooming in and out on features of interest (especially the craters), and measuring the coordinates of the centers and parts of the images (e.g., the crater walls and shadows). These kinds of measurements will be done in the steps below. This is your chance to explore the raw data and familiarize yourself with it before diving in to the more detailed analysis steps.