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A.
Safety stop
Figure 4. A
) Thread the counterweight shaft onto the mount.
B
) After removing the safety stop, slide the counterweight onto the
shaft.
IV. Understanding and
Using the Equatorial Mount
When you look at the night sky, you no doubt have noticed 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 is designed to compensate for that
motion, allowing you to easily "track" the movement of astro-
nomical 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.
Slow motion
cable
Figure 5.
Attach the two slow-motion cables to the mount.
B.
Saddle
clamp
knobs
Dec. slow-motion
cable
Figure 6.
The assembled EQ-13 mount looks like this.
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, also known as Polaris (see Figures 6 and
14). 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 14). The two stars at the end of the "bowl" of
the Big Dipper point approximately 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).
To polar align the equatorial mount:
1. Roughly level the mount by adjusting the length of the three
tripod legs as needed.
2. Loosen the latitude lock knob a half turn or so (Figure 15).
3. Using the two latitude adjustment T-bolts, set the latitude so
that the pointer on the latitude scale indicates the latitude
of your observing location. (Loosen one latitude adjustment
T-bolt before tightening the other.) If you don't know your
location's latitude, you can look it up on the internet. For
example, if your latitude is 35° North, set the pointer to 35.
Then retighten the latitude lock knob. The latitude setting
Dovetail
saddle
Dec. lock knob
R.A. lock knob
R.A. slow-motion
cable
5
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