Orion 100 EQ instruction manual Ight a, Polar Alignment

Declination setting circle

Declination lock lever

Front opening in R.A. axis

Latitude scale

Latitude adjustment

T-bolts

Azimuth fine adjustment knobs

	axis
D	eclination

Right Ascension lock lever

Right Ascension setting circle lock thumbscrew

R
ight A
scension	axis

Polar axis finder scope

Right Ascension setting circle

Figure 6. The equaltorial mount of the AstroView 100 EQ.

time. That apparent motion is caused by the Earth’s rotation (from west to east). An equatorial mount (Figure 6) 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 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.

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

Polar Alignment

For Northern Hemisphere observers, approximate polar align- ment is achieved by pointing the mount’s R.A. axis at the North Star, or 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 Polaris.

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).

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.

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).

2.Loosen one of the latitude adjusting T-bolts and tighten the other to tilt the mount until the pointer on the latitude scale is set at the latitude 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 setting 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 optical tube until it is parallel with the R.A. axis. The pointer on the Dec. setting circle should read 90°. Retighten the Dec. lock lever.

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