15
calibrating the right ascension setting circle
1. Identify a bright star in the sky near the celestial equator
(Dec. = 0°) and look up its coordinates in a star atlas.
2. Loosen the R.A. and Dec. lock knobs (23, 25) on the equa-
torial mount (5), so the telescope optical tube can move
freely.
3. Point the telescope at the bright star whose coordinates
you know. Lock the R.A. and Dec. lock knobs. Center the
star in the telescope’s field of view with the slow-motion
control cables.
4. Rotate the setting circle until the metal arrow indicates the
R.A. coordinate listed in the star atlas for the object.
Finding objects With the setting circles
Now that both setting circles are calibrated, look up in a star
atlas the coordinates of an object you wish to view.
Loosen the Dec. lock knob (25) and rotate the telescope until
the Dec. value from the star atlas matches the reading on the
Dec. setting circle (22). Remember that values of the Dec. set-
ting circle are positive when the telescope is pointing north of
the celestial equator (Dec. = 0°), and negative when the tele-
scope is pointing south of the celestial equator. Retighten the
lock knob.
Loosen the R.A. lock knob (23) and rotate the telescope until
the R.A. value from the star atlas matches the reading on the
R.A. setting circle (24). Remember to use the upper set of
numbers on the R.A. setting circle. Retighten the lock knob.
Most setting circles are not accurate enough to put an object
dead-center in the telescope’s eyepiece, but they should place
the object somewhere within the field of view of the EZ Finder
II (4), assuming the equatorial mount is accurately polar
aligned. Use the slow-motion controls to center the object in
the EZ Finder II, and it should appear in the telescope’s field
of view.
The R.A. setting circle must be re-calibrated every time you
wish to locate a new object. Do so by calibrating the setting
circle for the centered object before moving on to the next
one.
confused about Pointing the telescope?
Beginners occasionally experience some confusion about
how to point the telescope overhead or in other directions. In
Figure 1 the telescope is pointed north, as it would be during
polar alignment. The counterweight shaft is oriented down-
ward. But it will not look like that when the telescope is pointed
in other directions. Let’s say you want to view an object that is
directly overhead, at the zenith. How do you do it?
One thing you DO NOT do is make any adjustment to the lati-
tude adjustment T-bolt (30). That will nullify the mount’s polar
alignment. Remember, once the mount is polar aligned, the
telescope should be moved only on the R.A. and Dec. axes.
To point the scope overhead, first loosen the R.A. lock knob
(23) and rotate the telescope on the R.A. axis until the coun-
terweight shaft is horizontal (parallel to the ground). Then
loosen the Dec. lock knob (25) and rotate the telescope until it
is pointing straight overhead. The counterweight shaft (26) is
still horizontal. Then retighten both lock knobs.
Similarly, to point the telescope directly south, the counter-
weight shaft should again be horizontal. Then you simply
rotate the scope on the Dec. axis until it points in the south
direction.
What if you need to aim the telescope directly north, but at an
object that is nearer to the horizon than Polaris? You can’t do
it with the counterweight down as pictured in Figure 1. Again,
you have to rotate the scope in R.A. so the counterweight
shaft is positioned horizontally. Then rotate the scope in Dec.
so it points to where you want it near the horizon.
To point the telescope to the east or west, or in other direc-
tions, you rotate the telescope on its R.A. and Dec. axes.
Depending on the altitude of the object you want to observe,
the counterweight shaft will be oriented somewhere between
vertical and horizontal.
Figure 10 illustrates how the telescope will look pointed at the
four cardinal directions—north, south, east, and west
The key things to remember when pointing the telescope is
that a) you only move it in R.A. and Dec., not in azimuth or
latitude (altitude), and b) the counterweight and shaft will not
always appear as it does in Figure 1. In fact, it almost never
will!
5. using Your telescope
choosing an observing site
When selecting a location for observing, get as far away as
possible from direct artificial light such as street lights, porch
Figure 10a-d.
These illustrations show the telescope pointed in the four cardinal directions (a) north, (b) south, (c) east, (d) west. Note
that the tripod and mount have not been moved; only the telescope tube has been moved on the R.A. and Dec. axes.
a
b
c
d
