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Figure 3d. Balancing the telescope with respect to the Dec. axis.
As shown here, the telescope is out of balance (tilting).
Figure 3e. Telescope is now balanced on the Dec. axis, i.e., it
remains horizontal when hands
are released.
The telescope is now balanced on both axes. Now when you
loosen the lock thumb screw on one or both axes and manu-
ally point the telescope, it should move without resistance and
should not drift from where you point it.
6
5. 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 rota-
tion (from west to east). An equatorial mount (Figure 2) is
designed to compensate for that motion, allowing you to
easily "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 (polar) 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; this is a process called
polar alignment.
Polar Alignment
For Northern Hemisphere observers, approximate polar
alignment 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 4). 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.
2. Loosen the latitude lock t-bolt. Turn the latitude adjust-
ment t-bolt and tilt the mount until the pointer on the lati-
tude 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. Then retighten the latitude lock t-bolt.
The latitude setting should not have to be adjusted again
unless you move to a different viewing location some dis-
tance away.
3. Loosen the Dec. lock thumb screw and rotate the tele-
scope 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 thumb screw.
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