Use this spreadsheet to determine how accurate your mount/telescope is pointed at the celestial north pole.
Compass’ only tell us which direction the magnetic north pole is. Polaris (the “north” star) gives us a close (less than one degree) approximation. But to use a mount/telescope for taking images, you want to be parrallel within several arcminutes (or even arcseconds) of the celestial polar axis.
Before using this spreadsheet, determine how the knobs on your mount/telescope change the azimuth and altitude. For instance, if turning the altitude knob twenty turns changes the altitude five degrees you now know that the altitude changes 900 arcseconds for each turn, or 15 arcminutes for each turn. Likewise, determine the effect of the azimuth knob.
This spreadsheet is based on a paper written by Ralph Pass. It is included below the spreadsheet. Read the paper for an explanation of how to use this with a GoTo mount/telescope.
Use a sky program (like Stellarium – available at stellarium.org) to find out what the local sidereal hour angle is (what’s this? – SHA).
Put the SHA in the spreadsheet, along with your Latitude, and the coordinates of two identifiable stars. Follow the instructions in the PDF paper, and enter the error(s) you find when you slew to the second star.
The spreadsheet will then calculate the amount(s) and direction(s) your mount/telescope must be moved to point at the celestial pole. Then using the knob information you prepared earlier, make your mount/telescope corrections – wallah! See the original blog post for the link to the spreadsheet if it doesn’t show below.
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