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Now look through the finder scope. Is the object centered in
the finder scope's field of view, i.e., on the crosshairs? If not,
adjust the three finder scope alignment screws until it is cen-
tered. By loosening one alignment screw and tightening
another, you change the line of sight of the finder scope. The
plastic film lining the inside of the bracket barrel is designed
to prevent the alignment screws from marring the finish on
finder scope.
Once the target object is centered on the crosshairs of the
finder scope, look again in the main telescope's eyepiece and
see if it is still centered there as well. If it is not, repeat the
entire process, making sure not to move the main telescope
while adjusting the alignment of the finder scope.
Check the alignment by pointing the main telescope at anoth-
er object and centering it in the finder scope. Then look
through the main telescope eyepiece and see if the object is
centered. If it is, your job is done. If it isn't, make the neces-
sary adjustments to the finder scope's alignment screws until
the object is centered in both instruments.
Note that the image seen through the finder scope appears
upside down. This is normal for astronomical finder scopes.
5. Setting up and Using the
Equatorial Mount
When you look at the night sky, you have no doubt 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 is designed to follow
the motion of the stars, allowing you to easily keep astro-
nomical objects from drifting out of the telescope's field of
view when you're observing them.
The equatorial mount enables you to follow, or track, objects
by slowly rotating the telescope on its right ascension axis,
using only the R.A. slow-motion cable. But first the mount
must be aligned with the Earth's rotational axis.
For Northern Hemisphere observers, this is achieved by sim-
ply 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 2, page 10). 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 bare-
ly visible with the naked eye (magnitude 5.5). Consult a star
atlas or other reference book for instructions on polar-aligning
your telescope in the Southern Hemisphere.
Polar Alignment
For general visual observation, an approximate polar alignment
is sufficient. This must be done at night, when Polaris is visible.
1. Level the equatorial mount by adjusting the length of the
three tripod legs accordingly.
2. Loosen the latitude lock knob and tilt the mount until the
pointer on the latitude scale is set at the latitude of your
observing site. For example, if your latitude is 40° North,
set the pointer to 40. Then retighten the latitude lock knob.
If you don't know your latitude, consult a geographical
atlas to find it. 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 opti-
cal tube until it is parallel with the R.A. axis. The pointer on
the Dec. setting circle should read 90°. Retighten the Dec.
lock knob.
4. Next, loosen the azimuth lock knob at the base of the
equatorial mount. Rotate the entire equatorial mount in the
horizontal direction until the telescope (and R.A. axis)
points roughly at Polaris. If you cannot observe Polaris
directly from your observing site, consult a compass and
point the R.A. axis North. Retighten the azimuth lock knob.
The equatorial mount is now polar-aligned for casual observing.
More precise polar alignment is described in many amateur
astronomy reference books and astronomy magazines.
Note that 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 spoil the polar alignment.
The telescope should only be moved about its R.A. and
Dec. axes.
Tracking Celestial Objects
When you observe a celestial object through the telescope,
you'll see it drift slowly across the field of view. To keep it in
the field, if your equatorial mount is polar-aligned, just turn the
R.A. slow-motion control. The Dec. slow-motion control is not
needed for tracking. Objects will appear to move faster at
higher magnifications, because the field of view is narrower.
Understanding the Setting Circles
The setting circles on an equatorial mount enable you to
locate celestial objects by their "celestial coordinates." Every
object resides in a specific location on the "celestial sphere."
That location is denoted by two numbers: its right ascension
(R.A.) and declination (Dec.). In the same way, every location
on Earth can be described by its longitude and latitude. R.A.
is similar to longitude on Earth, and Dec. is similar to latitude.
The R.A. and Dec. values for celestial objects can be found in
any star atlas or star catalog.
The R.A. setting circle is scaled in hours, from 1 through 24,
with small hash marks in between representing 10-minute
increments (there are 60 minutes in 1 hour of R.A.). The num-
bers closest to the R.A. gear apply to viewing in the Southern
Hemisphere, while the numbers above them apply to viewing
in the Northern Hemisphere. The Dec. setting circle is scaled in
degrees (there are 60 arc-minutes in 1 degree of declination).
So, the coordinates for the Orion Nebula listed in a star atlas
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