9
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 21). 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 equatorial mount by adjusting the length
of the three tripod legs as needed.
2. Loosen the latitude lock knob (see
Figure 19). Turn the lati-
tude adjustment bolt until the pointer on the latitude scale
is indicating the latitude of your observing location (
Figure
15). If you don’t know your 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 should not have to be adjusted again unless
you move to a different viewing location some distance
away.
3. Loosen the Dec. lock knob and rotate the telescope optical
tube until it is parallel with the R.A. axis, as it is in
Figure
2. The pointer on the Dec. setting circle should read 90°.
Retighten the Dec. lock knob.
4. Loosen the azimuth lock knob at the base of the equatorial
mount (
Figure 7b) a half turn or so and rotate the mount
so the R.A. axis points roughly at Polaris. If you cannot see
Polaris directly from your observing site, consult a com-
pass and rotate the mount so the telescope points North.
Retighten the azimuth lock knob.
The equatorial mount is now polar aligned.
From this point
on in your observing session, you should not make any
further adjustments to 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.
Using the R.A. and Dec. Slow-Motion Control
Cables
The R.A. and Dec. slow-motion control cables allow fine
adjustment of the telescope’s position to center objects within
the field of view. Before using the cables, manually “slew” the
mount to point the telescope in the vicinity of the desired tar-
get. Do this by loosening the R.A. and Dec. lock knobs (
Figure
19) and moving the telescope about the mount’s R.A. and Dec.
Figure
20
.
Balancing the telescope about the
a)
R.A. and
b)
Dec. axes.
b.
a.
Big Dipper
(in Ursa Major)
Little Dipper
(in Ursa Minor)
Cassiopeia
N.C.P.
Pointer
Stars
Polaris
Figure 21.
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).