Orion Polar Alignment, To polar align the StarBlast 4.5 EQ, Tracking Celestial Objects

of astronomical objects, thereby keeping them from drifting out of the telescope’s field of view while you’re observing.

This is accomplished by slowly rotating the telescope on its right ascension (R.A.) axis, using only the R.A. slow-motion cable. But first the R.A. axis of the mount must be aligned with the Earth’s rotational (polar) axis—a process called polar alignment.

Polar Alignment

For Northern Hemisphere observers, approximate polar align- ment is achieved by pointing the mount’s right ascension axis at the North Star (Polaris). It lies within 1° of the north celestial 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 7). 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).

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

Figure 7. 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).

To polar align the StarBlast 4.5 EQ:

1.Level the equatorial mount by adjusting the length of the three tripod legs.

2.Loosen the latitude lock T-bolt. Turn the latitude adjustment T-bolt until the pointer on the latitude scale is indicating the latitude of your observing site. If you don’t know your lati- tude, consult a geographical atlas to find it. For example, if your latitude is 35° North, set the pointer to 35. Then retighten the latitude lock T-bolt. The latitude setting should not have to be adjusted again unless you move to a differ- ent viewing location some distance away.

3.Loosen the Dec. lock knob and rotate the telescope optical tube until it is parallel with the R.A. axis, as it is in Figure 1a. The pointer on the Dec. setting circle should read 90°.

Retighten the Dec. lock lever.

4.Loosen the azimuth lock knob at the base of the equa- torial mount and rotate the mount so the telescope tube (and R.A. axis) points roughly at Polaris. If you cannot see Polaris directly from your observing site, consult a com- pass and rotate the mount so the telescope points North. Retighten the azimuth lock knob.

The equatorial mount is now polar aligned. From this point on in your observing session, you should not make any further adjust- ments to the azimuth or the latitude of the mount, nor should you move the tripod. Doing so will undo the polar alignment. The tele- scope should be moved only about its R.A. and Dec. axes.

Use of the R.A. and Dec. Slow-Motion Control Cables

The R.A. and Dec. slow-motion control cables allow fine adjust- ment of the telescope’s position to center objects within the field of view. Before you can use the cables, you must manually “slew” the mount to point the telescope in the vicinity of the desired tar- get. Do this by loosening the R.A. and Dec. lock knobs and mov- ing the telescope about the mount’s R.A. and Dec. axes. Once the telescope is pointed somewhere close to the object to be viewed, retighten the mount’s R.A. and Dec. lock knobs.

The object should now be visible somewhere in the EZ Finder

II.If it isn’t, use the slow-motion controls to scan the surrounding area of sky. When the object is visible in the EZ Finder II, use the slow-motion controls to center the red dot on it. Now, look in the telescope’s eyepiece. If the EZ Finder II is properly aligned, the object should be visible somewhere in the field of view. Once the object is visible in the eyepiece, use the slow-motion controls to center it in the field of view.

The Dec. slow-motion control cable can move the telescope a maximum of 25°. This is because the Dec. slow-motion mecha- nism has a limited range of mechanical travel. (The R.A. slow- motion mechanism has no limit to its amount of travel.) If you can no longer rotate the Dec. control cable in a desired direction, you have reached the end of travel, and the slow-motion mechanism must be reset. This is done by first rotating the control cable sev- eral turns in the opposite direction from which it was being turned. Then, manually slew the telescope closer to the object you wish to observe (remember to first loosen the Dec. lock knob). You should now be able to use the Dec. slow-motion control cable again to fine adjust the telescope’s position.

Tracking Celestial Objects

When you observe a celestial object through the telescope, you’ll see it drift slowly across the field of view. To keep it in the field, assuming your equatorial mount is polar aligned, just turn the R.A. slow-motion control cable clockwise. The Dec. slow-motion control cable is not needed for tracking. Objects will appear to move faster at higher magnifications, because the field of view is narrower.

Optional Electronic Drives for Automatic Tracking

An optional DC electronic drive can be mounted on the R.A. axis of the equatorial mount to provide hands-free tracking. Objects will then remain stationary in the field of view without any manual adjustment of the R.A. slow-motion control cable.

7