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aligned, the object should be visible somewhere in the field
of view.
Once the object is visible in the telescope’s eyepiece, use
the slow-motion controls to center it in the field of view. You
can now switch to a higher magnification eyepiece, if you
wish. After switching eyepieces, you can use the slow-motion
control cables to re-center the image, if necessary.
The Dec. slow-motion control cable can move the telescope
a maximum of 25°. This is because the Dec. slow-motion
mechanism 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 should be reset. This is done by
first rotating the control cable several turns in the opposite
direction from which it was originally 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, 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 can be mounted on the R.A. axis
of 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.
Understanding the Setting Circles
The setting circles on an equatorial mount enable you to
locate celestial objects by their “celestial coordinates”. Every
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.
The R.A. setting circle is scaled in hours, from 1 through 24,
with small marks in between representing 10-minute incre-
ments (there are 60 minutes in 1 hour of R.A.). The lower
set of numbers (closest to the plastic R.A. gear cover) apply
to viewing in the Northern Hemisphere, while the numbers
above them apply to viewing in the Southern Hemisphere.
The Dec. setting circle is scaled in degrees, with each mark
representing 1° increments. Values of Dec. coordinates
range from +90° to -90°. The 0° mark indicates the celestial
equator. When the telescope is pointed north of the celestial
equator, values of the Dec. setting circle are positive, and
when the telescope is pointed south of the celestial equator,
values of the Dec. setting circle are negative.
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 (there are 60 arc-
minutes in 1 degree of declination).
Before you can use the setting circles to locate objects, the
mount must be well polar aligned, and the R.A. setting circle
must be calibrated. The Dec. setting circle has been perma-
nently calibrated at the factory, and should read 90° when-
ever the telescope optical tube is parallel with the R.A. axis.
Calibrating the Right Ascension Setting Circle
1. Identify a bright star near the celestial equator (Dec. = 0°)
and look up its coordinates in a star atlas.
2. Loosen the R.A. and Dec. lock knobs on the equatorial
mount, so the telescope optical tube can move freely.
3. Point the telescope at the bright star near the celestial
equator whose coordinates you know. Lock the R.A. and
Dec. lock knobs. Center the star in the telescope’s field of
view with the slow-motion control cables.
4. Loosen the thumb screw located just above the R.A. set-
ting circle pointer; this will allow the setting circle to rotate
freely. Rotate the setting circle until the pointer indicates
the R.A. coordinate listed in the star atlas for the object.
Retighten the thumb screw.
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 knob and rotate the telescope until
the Dec. value from the star atlas matches the reading on
the Dec. setting circle. Remember that values of the Dec.
setting circle are positive when the telescope is pointing
north of the celestial equator (Dec. = 0°), and negative
when the telescope is pointing south of the celestial
equator. Retighten the lock knob.
2. Loosen the R.A. lock knob and rotate the telescope until
the R.A. value from the star atlas matches the reading
on the R.A. setting circle. Remember to use the lower set
of numbers on the R.A. setting circle. Retighten the lock
knob.
Most setting circles are not accurate enough to put an object
dead-center in the telescope’s eyepiece, but they should
place the object somewhere within the field of view of the
finder scope, assuming the equatorial mount is accurately
polar aligned. Use the slow-motion controls to center the
object in the finder scope, and it should appear in the tele-
scope’s field of view.
Содержание AstroView 90mm EQ 9024
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