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Online Lunar Laser Ranging Pointing Service

  1. Select File → Data → Analyze: Choose the moon you observed from the Select menu.
  2. Select Plot → Plot Type → Connect Points: This will display a jagged, “connect-the-dots” version of your graph. When this graph of data points appears, try to find a pattern by eye, and take note of any data points that seem to be out of place.
  3. Select Plot → Fit Sine Curve → Set Initial Parameters: You are being asked to provide the program with initial values to use so that it can accurately construct a smooth sine curve to fit your data. Use the graph to find values for T-zero and Period.
  4. Determine T-zero: Click on a point at which the line connecting the data crosses from negative to positive. (If this happens several times, choose a point toward the left of the screen.) A date and a value very close to zero should appear in the box marked Cursor Value. Enter the date as your T-zeroparameter.
  5. Calculate the Period: Go back to the graph and find the next point at which the line passes from negative to positive (that is, when the moon has completed one full orbit). Subtract the earlier date from the later date and enter this as Period in the dialog box. If the line does not cross from negative to positive twice, use the interval between any two crossings as a good estimate of half the period and then double it. If it is convenient, you can count the number of days of one period directly on the screen, but you will probably have to make an estimate.
  6. Estimate the Amplitude: Click on the highest or lowest peak of your graph and read the value in the Cursor Position box. The Amplitude is equal to the absolute value of the highest peak or the lowest valley of your graph.
  7. Click OK: A blue sine curve will appear. It should be a rough fit for all your data points. If not, you may need to repeat the Set Initial Parameters step. If only one or two points are significantly off the blue line, they may represent inaccurate measurements.
  8. Refine the curve fit: Three scroll bars have appeared: T-Zero, Period, and Amplitude. Adjust each individually until your curve matches your data.
  9. Adjust the T-Zero point: As you adjust this value, the entire curve will slide to the left or right. Try to achieve the best fit for the data points closest to the T-zero value you selected above. At this stage, pay no attention to the number labeled RMS Residual; just use your eyes. After you’ve adjusted the T-zero value, you may notice that the points farther away from your T-zero point no longer fit as well.
  10. Fit the Period: Scroll to stretch or shrink the curve and achieve a better fit. If at any time you cannot scroll far enough to get a good fit, select Plot → Reset Scrollbars → Normal Sensitivity to re-center the bars.