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• Unlock the R.A. lock (22, Fig. 1) and the Dec. lock (23, Fig. 1) so that the telescope turns freely
on both axes. Then point the main telescope at some well-defined land object (e.g. the top of a
telephone pole) at least 200 yards distant, and re-lock the R.A and Dec. axes. Turn the flexible
cable controls, (3, Fig. 1) and (4, Fig. 1), to center the object in the telescopic field.
• With the front of the viewfinder already centered in the front bracket ring, look through the
viewfinder and loosen or tighten, as appropriate, one or more of the rear viewfinder bracket ring
thumbscrews (26, Fig. 1) until the viewfinder’s crosshairs are likewise centered on the object
previously centered in the main telescope.
• Check this alignment on a celestial object, such as a bright star or the Moon, and make any
refinements necessary, using the method outlined above.
With this alignment performed, objects first located in the wide-field viewfinder will also be centered in
the main telescope’s field of view. (Note: The viewfinder presents an image which is upside-down.)
UNDERSTANDING CELESTIAL MOVEMENTS AND COORDINATES
Understanding where to locate celestial objects, and how those objects move across the sky is
fundamental to enjoying the hobby of astronomy. Most amateur astronomers adopt the simple practice
of “star-hopping” to locate celestial objects by using star charts or astronomical software which identify
bright stars and star patterns (constellations) that serve as “road maps” and “landmarks” in the sky.
These visual reference points guide amateur astronomers in their search for astronomical objects. And,
while star-hopping is the preferred technique, a discussion of using setting circles for locating objects
is desirable since your telescope is provided with this feature. However, be advised, compared to star
hopping, object location by use of setting circles requires a greater investment in time and patience to
achieve a more precise alignment of the telescope’s polar axis to the celestial pole. For this reason, in
part, star-hopping is popular because it is the faster, easier way to become initiated in the hobby.
Understanding how astronomical objects move: Due to the Earth’s rotation, celestial bodies appear
to move from East to West in a curved path through the skies. The path they follow is known as their
line of Right Ascension (R.A.). The angle of this path they follow is known as their line of Declination
(Dec.). Right Ascension and Declination is analogous to the Earth-based coordinate system of latitude
and longitude.
Understanding celestial coordinates: Celestial objects are mapped according to the R.A. and Dec.
coordinate system on the “celestial sphere” (Fig. 2), the imaginary sphere on which all stars appear to
be placed. The Poles of the celestial coordinate system are defined as those 2 points where the Earth's
rotational axis, if extended to infinity, North and South, intersect the celestial sphere. Thus, the North
Celestial Pole is that point in the sky where an extension of the Earth's axis through the North Pole
intersects the celestial sphere. In fact, this point in the sky is located near the North Star, or Polaris.
On the surface of the Earth, “lines of longitude” are drawn between the North and South Poles.
Similarly, “lines of latitude” are drawn in an East-West direction, parallel to the Earth's equator. The
celestial equator is simply a
projection of the Earth's equator
onto the celestial sphere. Just as on
the surface of the Earth, imaginary
lines have been drawn on the
celestial sphere to form a
coordinate grid. Celestial object
positions on the Earth's surface are
specified by their latitude and
longitude.
The celestial equivalent to Earth
latitude is called “Declination,” or
simply “Dec,” and is measured in
degrees, minutes and seconds
north ("+") or south ("-") of the
celestial equator. Thus any point on
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23
0
1
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Rotation de la Terre
0° Déc.
Pôle céleste Sud.
Ascension droite
Etoile
Equateur céleste
Déc.-90° Déc.
+90° Déc.
Pôle nord céleste
D
é
c
l
i
n
a
i
s
o
n
Fig. 2: Celestial Sphere.
North Celestial Pole
(Vicinity of Polaris)
+90° Dec.
Star
Celestial
Equator
-90° Dec.
South
Celestial
Pole