Adjust Telescope Pointing

The 20-inch telescope uses disk driven encoders that slip a few arc seconds during a night of observing (usually in the same direction, it seems) and need to be reset at every night.

1. In the PT Target Selection window:
   • Set "Minimum Airmass" to 1.0
   • Set "Maximum Airmass" to 1.2
   • Make sure that only the FK5 box is checked
   • Click "Update."

   In a few seconds a list of pointing stars will appear.

2. Select an FK5 star with the middle mouse button. It will appear in the lower window.
   (Remove stars by double clicking with the middle mouse button.)
3. Make sure that:
   • "Dome frames" is 0
   • "Bias frames" is 0
   • The FK5 star is the only target in the lower window.

4. Click "Observe."
5. When the exposure log entry appears, double-click on, or carefully drag the cursor over, its exposure number. Then click "Display Selected Image."
6. Adjust the scaling and zoom in the fSAOimage display to find the star. If the star doesn't appear, try selecting a different one and doing the above again. If you still can't find a star, you'll need to initialize the telescope pointing with the bubble level.
7. Click "Fix Pointing." A dialog box prompting for the row and column of your FK5 star will appear. (Dialog boxes sometimes pop up underneath other windows so you may have to seach for it.)
8. Load the star position into the dialog box:
   • Click the "cursor" button in the fSAOimage window
   • Click the FK5 star with the middle mouse button.

9. Verify that the row and column are correct and click "okay." (Note that it's row-column, not X-Y.)
10. Click "okay" in the confirmation dialog box that pops up. The telescope will move a bit and reset its coordinates
11. Verify the telescope pointing by picking and observing a different FK5 star. Don't worry if the next star isn't precisely in the center of the CCD (but it should be close).
12. Check the output of hoggpt periodically. If there is an error in pointing, hoggpt won't find stars to measure. Of course other problems can cause hoggpt to fail, but pointing problems will show up here as well.

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