Orion SPACEPROBE 130ST EQ - Manual (Page 7)

Focusing the Finder Scope
If, when looking through the finder scope, the images appear
somewhat out of focus, you will need to refocus the finder
scope for your eyes. Loosen the lock ring located behind
the objective lens cell on the body of the finder scope (see
Figure 3a). Back the lock ring off by a few turns, for now.
Refocus the finder scope on a distant object by threading the
objective lens cell in or out on the finder scope body. Precise
focusing will be achieved by focusing the finder scope on a
bright star. Once the image appears sharp, retighten the lock
ring behind the objective lens cell. The finder scope’s focus
should not need to be adjusted again.
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 (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
alignment is achieved by pointing the mount’s R.A. 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 rota-
tional 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 6). 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 knob and rotate the telescope opti-
cal tube until it is parallel with the R.A. axis, as it is in
Figure 1. 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 equato-
rial 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
compass and rotate the mount so the telescope points
North. Retighten the azimuth lock knob.
The equatorial mount is now polar aligned for casual observ-
ing. More precise polar alignment is recommended for astro-
photography.
From this point on in your observing session, you should not
make any further adjustments in the azimuth or the latitude
of the mount, nor should you move the tripod. Doing so will
undo the polar alignment. The telescope should be moved
only about its R.A. and Dec. axes.
7
Big Dipper
(in Ursa Major)
Little Dipper
(in Ursa Minor)
N.C.P.
Pointer Stars
Polaris
Cassiopeia
Figure 6. 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).