Rough polar alignment
Polar alignment of your equatorial mount can be done in several ways. The easiest way is to use your latitude. The polar axis of an equatorially mounted scope must point at or be polar-aligned to the north celestial pole, the point in the sky around which all the other stars appear to rotate. The pole is directly above the north point on the horizon. So your axis must point both north and also be tilted up at an angle. Since the altitude of the north celestial pole is always equal to your latitude on the earth, you can just use the scope’s latitude adjustment to raise the polar axis to the right angle. Your latitude will equal the altitude of the north celestial pole. Either look on a map, use Google Earth or an almanac to find your observing site’s latitude. Unlock any latitude adjustment screws on the sides of the mount and turn the latitude adjustment screws until the index on the polar axis reads your latitude. Tighten the adjustment screws if needed to secure the latitude setting. (You may also need to loosen the center pivot bolt by turning the hex nut to allow the equatorial mount head to be tilted.) Now complete the polar alignment by turning the entire mount (not either axis – both should be clamped tightly) to align the upwards end of the polar axis with north on the horizon. If doing this at night, north is located directly below Polaris, the Pole Star. Another frequently used method is to point to Polaris. This star is located only one degree from the north celestial pole, the point in the sky around which all the other stars appear to rotate, and where the polar axis of a properly aligned equatorial mount should point. First, set up the mount so that the polar axis is pointing north. Second, unlock the declination clamp and move the scope in declination so that the tube is parallel to the polar axis. Your declination setting circles should read 90 degrees in this orientation. Clamp the declination lock. The last steps involve moving the entire mount. Don’t use either the RA or Dec motions to change the position of the tube. Third, move the mount in altitude and azimuth until Polaris is in your finder’s field of view or centered in your finderscope. Fourth, tweak the position of the mount by again moving the mount, this time centering Polaris in the eyepiece field of view. Altitude can be adjusted using the latitude adjustment screw or shortening-lengthening tripod legs. The alignment is now good enough for visual purposes. To refine this alignment, get a chart showing the offset of Polaris from the pole and move the mount so that this point in the sky is centered in the eyepiece field of view. You now have an excellent polar alignment well within one degree of the true north celestial pole.
Created On: Feb 21 2005 08:05 AM