Orion 9829 instruction manual Setting Up and Using the Equatorial Mount, Polar Alignment

Dec. slow-motion control knob

Dec. setting circle

Front opening		R.A.						Dec. lock lever
								R.A. lock lever
R.A. slow-motion		setting circle
control knob					Polar axis
			finder scope
					(optional)
			Latitude scale
						Latitude
a.				adjustment			b.
						L-bolts
	Figure 4. The SkyView Pro Equatorial Mount, shown from both sides.

4.To balance the telescope on the declination axis, first tight- en the R.A. lock lever, with the counterweight shaft still in the horizontal position.

5.With one hand on the telescope optical tube, loosen the Dec. lock lever. The telescope should now be able to rotate freely about the Dec. axis. Loosen the tube ring clamps a few turns, until you can slide the telescope tube forward and back inside the rings. (this can be aided by using a slight twisting motion on the optical tube while you push or pull on it). (Figure 3c).

6.Position the telescope in the tube rings so it remains hori- zontal when you carefully let go with both hands. This is the balance point for the optical tube with respect to the Dec. axis (Figure 3d).

7.Retighten the knurled ring clamps.

The telescope is now balanced on both axes. When you loosen the lock lever on one or both axes and manually point the telescope, it should move without resistance and should not drift from where you point it.

6.Setting Up and Using the Equatorial Mount

When you look at the night sky, you no doubt have noticed that the stars appear to move slowly from east to west over time. That apparent motion is caused by the Earth’s rotation (from west to east). An equatorial mount (Figure 4) is designed to compensate for that motion, allowing you to easi- ly “track” the movement of astronomical objects, thereby keeping them from drifting out of your 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 knob. But first the R.A. axis of the mount must be aligned with the Earth’s rotational (polar) axis—a process called polar alignment.

		Little Dipper
		(in Ursa Minor)
	Big Dipper	N.C.P.
	(in Ursa Major)		Polaris
	ter
oin
P	tars		Cassiopeia
S

Figure 5. 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 5). 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 bare- ly 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.

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