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The telescope is now balanced on both axes. Now when
you loosen the lock knob on one or both axes and man-
ually point the telescope, it should move without
resistance and should not drift from where you point it.
5. Setting Up and Using
the Equatorial Mount
When you look at the night sky, you no doubt have
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
(Figure 3) is designed to compensate for that motion,
enabling you to easily "track" the movement of astro-
nomical objects, thereby keeping them from drifting out
of the telescope's field of view while you're observing.
This is accomplished by slowly rotating the telescope
on its right ascension (polar) axis, using only the R.A.
slow-motion cable. But first the R.A. axis of the mount
must be aligned with the Earth's rotational (polar)
axis—a process called polar alignment.
Polar Alignment
For Northern Hemisphere observers, approximate
polar alignment is achieved by pointing the mount's
R.A. axis at the North Star, or Polaris. It lies within 1
degree 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 pat-
tern of the Big Dipper (Figure 4). The two stars at the end
of the "bowl" of the Big Dipper point right to Polaris, which
lies at a distance of about five times the separation of the
two bowl stars.
Observers in the Southern Hemisphere aren't so fortu-
nate to have a bright star so near the south celestial
pole (SCP). The star Sigma Octantis lies about 1
degree from the SCP, but it is barely visible with the
naked eye (magnitude 5.5).
For general visual observation, an approximate polar
alignment is sufficient:
1. Level the equatorial mount by adjusting the length of
the three tripod legs.
2. Loosen the latitude lock t-bolt. Turn the latitude
adjustment t-bolt and tilt the mount until the pointer
on the latitude scale is set at the latitude of your
observing site. If you don't know your latitude, con-
sult a geographical atlas to find it. For example, if
your latitude is 35° North, set the pointer to +35.
Then retighten the latitude lock t-bolt. The latitude
setting should not have to be adjusted again unless
you move to a different viewing location some dis-
tance away.
3. Loosen the Dec. lock knob and rotate the telescope
optical 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. Loosen the azimuth lock knob and rotate the entire
equatorial mount left-to-right so the telescope tube
(and R.A. axis) points roughly at Polaris. If you can-
not see Polaris directly from your observing site,
consult a compass and rotate the equatorial mount
so the telescope points North. Retighten the azimuth
lock knob.
The equatorial mount is now approximately polar-
aligned for casual observing. More precise polar
alignment is required for astrophotography. Several
methods exist and are described in many amateur
astronomy reference books.
Note: 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 undo the polar align-
ment. The telescope should be moved only about its
R.A. and Dec. axes.
Tracking Celestial Objects
When you observe a celestial object through the tele-
scope, 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.
Optional Motor Drives for Automatic
Tracking and Astrophotography
An optional DC motor drive (EQ-2M, Orion part #7827)
can be mounted on the R.A. axis of the EQ-2 equatori-
al mount to provide hands-free tracking. Objects will
then remain stationary in the field of view without any
manual adjustment of the R.A. slow-motion control. The
motor drive is necessary for astrophotography.
Understanding the Setting Circles
The setting circles on an equatorial mount enable the
location of astronomical objects by their "celestial coor-
dinates." Every astronomical object resides in a specific
location on the "celestial sphere." That location is denot-
ed 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
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