Orion AstroView 9005 - Manual (Page 10)

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loosen the big tripod attachment knob directly underneath
the base of the equatorial mount. The fine adjustment knobs
work by loosening one and then tightening the other. When
done, retighten the tripod attachment knob to firmly secure
the mount and tripod.
Once Polaris is centered in the small circle, you are done. The
telescope is now accurately polar aligned, and can be used
for advanced observational applications, such as astropho-
tography or precise use of the manual setting circles. As
mentioned before, only move the telescope along the R.A.
and Dec. axes; if you move the tripod, or change the tilt of the
equatorial mount, you will need to polar align again.
Remember, accurate polar alignment is not needed for
casual visual observing. Most of the time, approximate polar
alignment, as outlined previously, will suffice.
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, 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 Drive
An optional DC motor drive system can be mounted on the
AstroView’s 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. The motor
drive system is necessary for astrophotography.
understanding the Setting Circles
The setting circles on an equatorial mount enable you to locate
celestial objects by their “celestial coordinates.” Every astronomi-
cal object resides in a specific location on the “celestial sphere.”
That location is denoted 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 to latitude. The R.A. and
Dec. values for celestial objects can be found in any star atlas or
star catalog.
So, the coordinates for the Orion Nebula listed in a star atlas
will look like this:
R.A. 5h 35.4m Dec. -5° 27’
That’s 5 hours and 35.4 minutes in right ascension, and -5
degrees and 27 arc-minutes in declination (the negative sign
denotes south of the celestial equator). There are 60 minutes
in 1 hour of R.A and there are 60 arc-minutes in 1 degree of
declination.
The telescope’s R.A. setting circle is scaled in hours, from 1
through 24, with small lines in between representing 10-min-
ute increments. The upper set of numbers apply to viewing in
the Northern Hemisphere, while the numbers below them
apply to viewing in the Southern Hemisphere. The Dec. set-
ting circle is scaled in degrees.
Before you can use the setting circles to locate objects, the
mount must be accurately polar aligned, and the setting cir-
cles must be calibrated. The declination setting circle was
calibrated at the factory, and should read 90° when the tele-
scope optical tube is pointing exactly along the R.A. axis.
Calibrating the right Ascension Setting Circle
1. Identify a bright star near the celestial equator and look up
its coordinates in a star atlas.
2. Loosen the R.A. and Dec. lock levers on the equatorial
mount, so the telescope optical tube can move freely.
3 Point the telescope at the bright star whose coordinates
you know. Center the star in the telescope’s eyepiece.
Lock the R.A. and Dec. lock levers.
4. Loosen the large thumbscrew just above the R.A. setting
circle and rotate the R.A. setting circle so the pointer indi-
cates the R.A. coordinate listed for the bright star in the star
atlas. Do not retighten the thumbscrew when using the
R.A. setting circles for finding objects; the thumbscrew is
only needed for polar alignment using the polar axis finder
scope.
Finding Objects With the Setting Circles
Now that both setting circles are calibrated, look up in a star
atlas the coordinates of an object you wish to view.
1. Loosen the Dec. lock lever and rotate the telescope until
the Dec. value from the star atlas matches the reading on
the Dec. setting circle. If the telescope is being aimed
toward the south and the Dec. setting circle pointer pass-
es the 0° indicator, the value on the Dec. setting circle
becomes a negative number. Retighten the lock lever.
2. Loosen the R.A. lock lever and rotate the telescope until
the R.A. value from the star atlas matches the reading on
the R.A. setting circle. Retighten the lock lever.
Most setting circles are not accurate enough to put an object
dead-center in your finder scope’s field of view, but they’ll get
you close, assuming the equatorial mount is accurately polar-
aligned. The R.A. setting circle should be recalibrated every
time you wish to locate a new object. Do so by calibrating the
setting circle for the centered object before moving on to the
next one.
Confused About Pointing the telescope?
Beginners occasionally experience some confusion about
how to point the telescope overhead or in other directions. In
Figure 1 the telescope is pointed north as it would be during
polar alignment. The counterweight shaft is oriented down-
ward. But it will not look like that when the telescope is pointed
in other directions. Let’s say you want to view an object that is
directly overhead, at the zenith. How do you do it?
One thing you DO NOT do is make any adjustment to the
latitude adjustment T-bolts. That will spoil the mount’s polar
alignment. Remember, once the mount is polar aligned, the
telescope should be moved only on the R.A. and Dec. axes.
To point the scope overhead, first loosen the R.A. lock lever
and rotate the telescope on the R.A. axis until the counter-