Orion starBlast 4.5 EQ - Manual (Page 7)

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of astronomical 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 (R.A.) 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 align-
ment is achieved by pointing the mount’s right ascension axis
at the North Star (Polaris). It lies within 1° 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 the NCP.
To find Polaris in the sky, look north and locate the pattern of the
Big Dipper (Figure 7). The two stars at the end of the “bowl” of the
Big Dipper point right to Polaris.
Observers in the Southern Hemisphere aren’t so fortunate to
have a bright star so near the south celestial pole (SCP). The star
Sigma Octantis lies about 1° from the SCP, but it is barely visible
with the naked eye (magnitude 5.5).
to polar align the starBlast 4.5 EQ:
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 until the pointer on the latitude scale is indicating the
latitude of your observing site. If you don’t know your lati-
tude, consult 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 differ-
ent viewing location some distance away.
3. Loosen the Dec. lock knob and rotate the telescope optical
tube until it is parallel with the R.A. axis, as it is in Figure
1a. The pointer on the Dec. setting circle should read 90°.
Retighten the Dec. lock lever.
4. Loosen the azimuth lock knob at the base of the equa-
torial mount and rotate the mount so the telescope tube
(and R.A. axis) points roughly at Polaris. If you cannot see
Polaris directly from your observing site, consult a com-
pass and rotate the mount so the telescope points North.
Retighten the azimuth lock knob.
The equatorial mount is now polar aligned. From this point on in
your observing session, you should not make any further adjust-
ments to the azimuth or the latitude of the mount, nor should you
move the tripod. Doing so will undo the polar alignment. The tele-
scope should be moved only about its R.A. and Dec. axes.
use of the r.a. and Dec. slow‑Motion control
cables
The R.A. and Dec. slow-motion control cables allow fine adjust-
ment of the telescope’s position to center objects within the field
of view. Before you can use the cables, you must manually “slew”
the mount to point the telescope in the vicinity of the desired tar-
get. Do this by loosening the R.A. and Dec. lock knobs and mov-
ing the telescope about the mount’s R.A. and Dec. axes. Once
the telescope is pointed somewhere close to the object to be
viewed, retighten the mount’s R.A. and Dec. lock knobs.
The object should now be visible somewhere in the EZ Finder
II. If it isn’t, use the slow-motion controls to scan the surrounding
area of sky. When the object is visible in the EZ Finder II, use the
slow-motion controls to center the red dot on it. Now, look in the
telescope’s eyepiece. If the EZ Finder II is properly aligned, the
object should be visible somewhere in the field of view. Once the
object is visible in the eyepiece, use the slow-motion controls to
center it in the field of view.
The Dec. slow-motion control cable can move the telescope a
maximum of 25°. This is because the Dec. slow-motion mecha-
nism has a limited range of mechanical travel. (The R.A. slow-
motion mechanism has no limit to its amount of travel.) If you can
no longer rotate the Dec. control cable in a desired direction, you
have reached the end of travel, and the slow-motion mechanism
must be reset. This is done by first rotating the control cable sev-
eral turns in the opposite direction from which it was being turned.
Then, manually slew the telescope closer to the object you wish
to observe (remember to first loosen the Dec. lock knob). You
should now be able to use the Dec. slow-motion control cable
again to fine adjust the telescope’s position.
tracking celestial objects
When you observe a celestial object through the telescope, you’ll
see it drift slowly across the field of view. To keep it in the field,
assuming your equatorial mount is polar aligned, just turn the
R.A. slow-motion control cable clockwise. The Dec. slow-motion
control cable is not needed for tracking. Objects will appear to
move faster at higher magnifications, because the field of view
is narrower.
optional Electronic Drives for automatic tracking
An optional DC electronic drive can be mounted on the R.A. axis
of the equatorial 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 cable.
Big Dipper
(in Ursa Major)
Little Dipper
(in Ursa Minor)
Cassiopeia
N.C.P.
Pointer
Stars
Polaris
Figure 7. To find Polaris in the night sky, look north and find the
Big Dipper. Extend an imaginary line from the two "Pointer Stars"
in the bowl of the Big Dipper. Go about five times the distance
between those stars and you'll reach Polaris, which lies within 1° of
the north celestial pole (NCP).