7
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 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.
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.
4. Move the tripod 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
Big Dipper
(in Ursa Major)
Little Dipper
(in Ursa Minor)
Cassiopeia
N.C.P.
Pointer
Stars
Polaris
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).
Figure 6.
The equaltorial mount of the AstroView 100 EQ.
Right Ascension lock lever
Right Ascension setting circle
lock thumbscrew
Polar axis finder scope
Right Ascension setting circle
Declination setting circle
Declination lock lever
Front opening
in R.A. axis
Latitude scale
Latitude adjustment
T-bolts
Azimuth fine
adjustment knobs
Right Ascension axis
Declination axis
