Precise Polar Alignment - Meade LX200 Instruction Manual

As an aside procedure, during your first use of the telescope,
you should check the calibration of the Declination setting
circle (3, Fig. 1), located at the top of each side of the fork.
After performing the polar alignment procedure, center the
star Polaris in the telescope field. Remove the knurled
central hub of the Declination setting circle and slightly
loosen the two bolts located under the knob. Now turn the
circle unit until it reads 89.2°, the Declination of Polaris, and
then tighten down the two bolts and replace the knurled
knob. Also realize, should you wish to use the manual setting
circles, that the R.A. setting circle (10, Fig. 1) must be
calibrated on the Right Ascension of a star (see APPENDIX C,
page 31) manually every time the telescope is set up. The
R.A. setting circle has two sets of numbers, the inner set is
for Southern hemisphere use, while the other is for Northern
hemisphere use.
Once the latitude angle of the wedge has been fixed and
locked-in according to the above procedure, it is not necessary
to repeat this operation each time the telescope is used, unless
you move a considerable distance North or South from your
original observing position. (Approximately 70 miles movement
in North-South observing position is equivalent to 1° in latitude
change). The wedge may be detached from the field tripod and,
as long as the latitude angle setting is not altered and the field
tripod is leveled, it will retain the correct latitude setting when
replaced on the tripod.

3. Precise Polar Alignment

It should be emphasized that precise alignment of the
telescope's polar axis to the celestial pole for casual visual
observations is not necessary. Don't allow a time-consuming
effort at lining up with the pole to interfere with your basic
enjoyment of the telescope. For long-exposure photography,
however, the ground rules are quite different, and precise polar
alignment is not only advisable, but almost essential.
Notwithstanding the precision and sophistication of the drive
system supplied with the Meade LX200 telescopes, the fewer
tracking corrections required during the course of a long-
exposure photograph, the better. (For our purposes, "long-
exposure" means any photograph of about 10 minutes duration
or longer). In particular, the number of Declination corrections
required is a direct function of the precision of polar alignment.
Precise polar alignment requires the use of a crosshair
eyepiece. The Meade Illuminated Reticle Eyepiece is well-
suited in this application, but you will want to increase the
effective magnification through the use of a 2X or 3X Barlow
lens. Then either follow Refined Polar Alignment (page 17) or
follow this procedure, sometimes better known as the "Drift"
method (particularly if the pole star is not visible):
a. Obtain a rough polar alignment as described earlier. Place
the illuminated reticle eyepiece (or eyepiece/Barlow
combination) into the eyepiece holder of the telescope.
b. Point the telescope, with the motor drive running, at a
moderately bright star near where the meridian (the North-
South line passing through your local zenith) and the
celestial equator intersect. For best results, the star
Polaris #
Fig. 22: Mount too far East.
# Polaris
Fig. 23: Mount too far West.
- 30 -
should be located within ±30 minutes in R.A. of the
meridian and within ±5° of the celestial equator. (Pointing
the telescope at a star that is straight up, with the
Declination set to 0°, will point the telescope in the right
direction.)
c. Note the extent of the star's drift in Declination (disregard
drift in Right Ascension):
a. If the star drifts South (or down), the telescope's
polar axis is pointing too far East (Fig. 22).
b. If the star drifts North (or up), the telescope's polar
axis is pointing too far West (Fig. 23).
d. Move the wedge in azimuth (horizontally) to effect the
appropriate change in polar alignment. Reposition the
telescope's East-West polar axis orientation until there is
no further North-South drift by the star. Track the star for
a period of time to be certain that its Declination drift has
ceased. (Please note that Figs. 22, 23, 24, and 25 show
the telescope pointed in the 90 degree position, and not
the 0 degree position that is required for "Drift" method
alignment. This is done to illustrate the position of the pole
star relative to the polar axis of the telescope.)
e. Next, point the telescope at another moderately bright star
near the Eastern horizon, but still near the celestial
equator. For best results, the star should be about 20° or
30° above the Eastern horizon and within ± 5° of the
celestial equator.
f. Again note the extent of the star's drift in Declination:
a. If the star drifts South, (or down) the telescope's
polar axis is pointing too low (Fig. 24).
b. If the star drifts North, (or up) the telescope's polar
axis is pointing too high (Fig. 25).
g. Use the latitude angle fine-adjust control on the wedge to
effect the appropriate change in latitude angle, based on
your observations above. Again, track the star for a period
of time to be certain that Declination drift has ceased.
The above procedure results in very accurate polar alignment,
and minimizes the need for tracking corrections during
astrophotography.
Polaris #
Fig. 24: Mount too low.
Polaris #
Fig. 25: Mount too high.