Orion SIRIUS 9995 - Manual (Page 5)

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have either too much or too little counterweight. Remove
counterweight, or add optional counterweights if needed.
3. Retighten the counterweight lock knob. The telescope is
now balanced on the right ascension axis.
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 declination axis.
6. Loosen the knurled ring clamps on the tube rings 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 4c). If the mounting plate is connected directly
to your telescope’s tube (i.e. tube rings are not utilized), you
can balance the telescope in Dec. by sliding the mounting
plate forward or back in the slot on top of the equatorial
mount.
7. 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 4d).
8. Retighten the knurled ring clamps.
The telescope is now balanced on both axes. When you loos-
en 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 5) is designed
to compensate for that motion, allowing you to easily “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 the built in motor drive. 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, 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.
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).
Big Dipper
(in Ursa Major)
Little Dipper
(in Ursa Minor)
Cassiopeia
N.C.P.
Pointer
Stars
Polaris
Figure 5. The Sirius EQ-G mount.
Polar axis finder scope
Latitude scale
Latitude adjustment
L-bolts
Dec lock lever
Front opening
Right
Ascension
(R.A.)
axis
R.A. lock lever
Declination
(Dec)
axis
Figure 4a‑d. Proper operation of the equatorial mount requires
that the telescope tube be balanced on the R.A. and Dec. axes. (a)
With the R.A. lock lever released, slide the counterweight down the
counterweight shaft until it just counterbalances the telescope tube.
(b) When you let go with both hands, the tube should not drift up or
down. (c) With the Dec. lock lever released, loosen the tube ring lock
clamps a few turns and slide the telescope forward or back in the
tube rings. (d) When the tube is balanced about the Dec. axis, it will
not move when you let go.
a. b.
c. d.