Polar Alignment, Using the Polar Axis Finder Scope

		Little Dipper
		(in Ursa Minor)
Big Dipper		N.C.P.
Big Dipper
(in Ursa Major)			Polaris
(in Ursa Major)

ointer
P	rs		Cassiopeia
ta
S

Figure 8. To find Polaris in the night sky, look north and find the Big Dipper. Extend an imaginary line from the two “Pointer Stars” in the bowl of the Big Dipper. Go about five times the distance between those stars and you'll reach Polaris, which lies within 1° of the north celestial pole (NCP).

Polar Alignment

For Northern Hemisphere observers, approximate polar align- ment is achieved by pointing the mount’s right ascension axis at the North Star, or Polaris. It lies within 1° of the north celes- tial pole (NCP), which is an extension of the Earth’s rotational axis out into space. Stars in the Northern Hemisphere appear to revolve around the NCP.

To find Polaris in the sky, look north and locate the pattern of the Big Dipper (Figure 8). The two stars at the end of the “bowl” of the Big Dipper point right to Polaris.

Observers in the Southern Hemisphere aren’t so fortunate to have a bright star so near the south celestial pole (SCP). The star Sigma Octantis lies about 1° from the SCP, but it is barely visible with the naked eye (magnitude 5.5).

For general visual observation, an approximate polar align- ment is sufficient.

1.Level the equatorial mount by adjusting the length of the three tripod legs. Temporarily remove the optical tube and counterweights from the mount before attempting to do this.

2.There are two altitude adjusting L-bolts (see Figure 7); loosen one while tightening the other. By doing this you will adjust the latitude of the mount. Continue adjusting the mount until the pointer on the latitude scale is set at the lat- itude of your observing site. If you don’t know your latitude, consult a geographical atlas to find it. For example, if your latitude is 35° North, set the pointer to 35. The latitude set- ting should not have to be adjusted again unless you move to a different viewing location some distance away.

3.Loosen the Dec. lock lever and rotate the telescope’s opti- cal tube until it is parallel with the right ascension axis, as it is in Figure 7.

4.Move the tripod so the telescope tube and right ascension axis point roughly at Polaris. If you cannot see Polaris directly from your observing site, consult a compass and rotate the tripod so the telescope points north.

The equatorial mount is now polar aligned for casual observing. More precise polar alignment is recommended for astrophotog- raphy. For this we recommend using the polar axis finder scope

Eyepiece	Alignment	Focus	Objective
focus ring	setscrew (3)	lock ring	lens
focus ring	setscrew (3)	lock ring	lens

Figure 9. The optional polar axis finder scope.

From this point on in your observing session, you should not make any further adjustments to the latitude of the mount, nor should you move the tripod. Doing so will undo the polar align- ment. The telescope should be moved only about its R.A. and Dec. axes.

Using the Polar Axis Finder Scope

The Atlas EQ mount comes with a polar axis finder scope (Figure 9) housed inside the right ascension axis of the mount. When properly aligned and used, it makes accurate polar alignment quick and easy to do.

Alignment of the Polar Axis Finder Scope

1.Loosen the Dec. lock lever and rotate the optical tube on the declination axis so that the tube is at a 90° to the right ascension axis (Figure 10). Tighten the Dec. lock lever.

2.Look through the polar finder at a distant object (during the day) and center it in the crosshairs. You may need to adjust the latitude adjustment L-bolts and the tripod position to do this.

3.Rotate the mount 180° about the R.A. axis. Again, it may be convenient to remove the counterweights and optical tube first.

4.Look through the polar finder again. Is the object being viewed still centered on the crosshairs? If it is, then no fur- ther adjustment is necessary. If not, then look through the polar finder while rotating the mount about the R.A. axis. You will notice that the object you have previously centered moves in a circular path. Use the three alignment setscrews on the polar axis finder (Figure 9) to redirect the crosshairs of the polar finder to the apparent center of this circular path. Repeat this procedure until the position that the crosshairs point to does not rotate off-center when the mount is rotated in R.A.

The polar axis finder scope is now ready to be used. When not in use, replace the plastic protective cover to prevent the polar finder from getting bumped.

Using the Polar Axis Finder Scope

The reticle of the polar axis finder scope for the Atlas has a tiny star map printed on it that makes precise polar alignment