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LX 200 Polar Alignment

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Posted by Daniel Johnson on October 4, 2002 12:39:57 UTC

I have not found the various polar alignment modes in Autostar to be very useful, so I have another trick. It's wordy, but easy once you grasp it. The key lies in realizing that your scope always wakes up thinking it is pointed in the "park scope" position, and believing that it knows where all the stars are. You let it point at one star of your choice (it will be wrong), and then at Polaris, and in each case you move the scope so that it is in fact pointed at those stars. Here are the details for my rough polar alignment for LX 200 GPS or original Autostar:
1) First, before you turn on the scope, adjust your wedge so that the fork arms point roughly at the north celestial pole, i.e. the polar axis points near Polaris-get as close as possible, but perfection at this point is not mandatory. 2) Now, before you turn on the scope in polar mode, unlock the axes and orient the scope so that it "wakes up" pointing at zero degrees declination (not at Polaris, but 90 degrees south of it, with the optical tube roughly perpendicular to the fork arms), and at the meridian (not at the east or west horizon, but up)-this is the "park scope" position that the scope THINKS it is in when it wakes up. Lock the axes in this position and turn the scope on. Let it do its GPS connection, or enter the date and time manually. 3) Without doing any further alignment, put the menu on "Select Object," then enter "Star", then "Named," then select some star you can actually see, preferably not near Polaris. Press Enter, then Go To. The scope may slew to some seemingly random spot, but it will probably be near the star you named. No matter how far off it is, unlock both axes, manually turn the scope on its axes (do not use the keypad for this movement yet) until the star you named is in the field of view, and lock the axes again with the star in the field. Now press ENTER and hold it for two seconds, then release. The display should say, "press enter to synch." Center the star carefully using the arrow buttons on the keypad, then press Enter. The scope now thinks it is polar aligned and synched on the star. It isn't quite, yet.
4) Now set the menus to Star, Named, Polaris, Enter, Go To. Let it slew to where it thinks Polaris is-it will be close, if you've done the above steps well, though Polaris may not quite be in the field of view. Now use the controls on your wedge (DO NOT MOVE THE KEYPAD OR SCOPE AXES) to center Polaris carefully. Now you are closer to polar aligned, and the better you did originally in step 1, the closer you are now. To get still closer, you will probably need to repeat steps 3 and 4. If you were way off in step 1, you may have to repeat steps 3 and 4 yet again. This approach isn't perfect, but it gets you close in 5 minutes or so, with practice-plenty good enough for visual observations. And there's no need to get your optical tube perfectly parallel with the fork axes at the beginning, though you may find that temporarily pointing the tube roughly parallel to the axes so that you can center Polaris in the finder (or Telerad) helps in getting step 1 right.
If you want alignment close enough for long-exposure photography, at this point you need to do the drift method, but the 5-minute drill just described will make it quicker by far. For the drift method, and also for another rough alignment method vaguely similar to the one I've described above, visit http://www.astrocruise.com/polarnew.htm--I do not know the authors of that page, but it is comprehensive.
If you've done the drift method once and done it perfectly, and can leave your wedge bolted in place on your pier, you shouldn't have to adjust your wedge for months. Just plop the scope back on the pier, repeat steps 2 and 3, and you will be perfectly aligned in under 5 minutes. Or if you can leave the scope on the pier permanently, then at the end of the night set the menu to Utilities, Park Scope. The scope will then wake up either perfectly aligned, or close enough that only step 3 is needed to regain excellent alignment-skip the alignment options offered on the keypad when the scope wakes up.
And if you can't leave the wedge on the pier, then dream up some way to be sure it's placed back on the pier the same every time. I don't have a permanent pier, just wheels on my tripod. I set up over the exact same spot each time. My friend Mike Vollmer taught me a method with a laser. I have a cheap laser on my wedge on the polar plate (the plate the scope attaches to). When I am perfectly aligned, the laser dot falls on a mark on my driveway 5 meters south of the scope. It is best to have the laser aim north or south, and 5 meters or more away. So I wheel my scope out over its exact spot, turn on the laser, and there I am-I know the polar alignment is the same as on the very first night I ever used the laser, when I did the job well.
P.S. If the scope won't track, be sure it isn't set for terrestrial objects (somewhere in the Setup menu). It may have come that way from the factory.

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