the celestial equator (which passes, for example, through the constellations Orion, Virgo and Aquarius)
is specified as having 0°0'0" Declination. The Declination of the star Polaris, located very near the
North Celestial Pole, is +89.2°.
The celestial equivalent to Earth longitude is called “Right Ascension,” or “R.A.” and is measured in
hours, minutes and seconds from an arbitrarily defined “zero” line of R.A. passing through the
constellation Pegasus. Right Ascension coordinates range from 0hr 0min 0sec up to (but not including)
24hr 0min 0sec. Thus there are 24 primary lines of R.A., located at 15 degree intervals along the
celestial equator. Objects located further and further east of the prime (0h 0m 0s) Right Ascension grid
line carry increasing R.A. coordinates.
With all celestial objects therefore capable of being specified in position by their celestial coordinates
of Right Ascension and Declination, the task of finding objects (in particular, faint objects) in the
telescope is vastly simplified. The setting circles, R.A (27, Fig. 1) and Dec. (28, Fig. 1) of the Polaris
114 EQ-D telescope may be dialed, in effect, to read the object coordinates and the object found
without resorting to visual location techniques. However, these setting circles may be used to
advantage only if the telescope is first properly aligned with the North Celestial Pole.
LINING UP WITH THE CELESTIAL POLE
Objects in the sky appear to revolve around the celestial pole. (Actually, celestial objects are essentially
“fixed,” and their apparent motion is caused by the Earth’s axial rotation). During any 24 hour period,
stars make one complete revolution about the pole, making concentric circles with the pole at the
center. By lining up the telescope’s polar axis with the North Celestial Pole (or for observers located in
Earth’s Southern Hemisphere with the South Celestial Pole), astronomical objects may be followed, or
tracked, by moving the telescope about one axis, the polar axis.
If the telescope is reasonably well aligned with the pole, therefore, very little use of the telescope’s
Declination flexible cable control is necessary and virtually all of the required telescope tracking will be
in Right Ascension. (If the telescope were perfectly aligned with the pole, no Declination tracking of
stellar objects would be required). For the purposes of casual visual telescopic observations, lining up
the telescope’s polar axis to within a degree or two of the pole is more than sufficient: with this level of
pointing accuracy, the telescope can track accurately by slowly turning the telescope’s R.A. flexible
cable control and keep objects in the telescopic field of view for perhaps 20 to 30 minutes.
To line up the Jupiter 114 EQ-D with the pole, follow this procedure:
1. Release the Azimuth lock (30, Fig. 1) of the Azimuth base (33, Fig. 1), so that the entire telescope-
with-mounting may be rotated in a horizontal direction. Rotate the telescope until the polar axis (10,
Fig. 1) points due North. Locate Polaris, the North Star (see Fig. 3), as an accurate reference for
due North.
2. Level the mount, if necessary, by adjusting
the heights of the three tripod legs. Set the
Dec dial to 90°.
3. Determine the latitude of your observing
location by checking a road map or atlas.
Release the latitude lock (9, Fig. 1) and tilt the
telescope mount with the latitude adjustment
knob (11, Fig. 1) so that the pointer indicates
the correct latitude of your viewing location on
the latitude scale (29, Fig. 1). Re-tighten the
latitude lock (9, Fig. 1).
4. Without moving the telescope on the Right Ascension and Declination axes, loosen the azimuth
and latitude locks (9 and 30, Fig. 1) and adjust the telescope until Polaris is centered in the
telescope eyepiece. If steps 1 - 3 above were performed with reasonable accuracy, your telescope
is now sufficiently well-aligned to the North Celestial Pole for visual observations.
Once the mount has been polar-aligned as described above, the latitude angle need not be adjusted
again, unless you move to a different geographical location (i.e. a different latitude). The only polar
alignment procedure that need be done each time you use the telescope is to point the polar axis due
North, as described in step 1 above.
– 9 –
Polaire
Grande Ourse
Petite Ourse
Cassiopée
Fig. 3: Locating Polaris.
Little Dipper
Polaris
Big Dipper
Cassiopeia
