7
to about where it was pointed before the slow-motion cable
stopped turning. Now you should be able to use the slow
motion cable again for ne pointing in either direction.
Tracking Celestial Objects
When you observe a celestial object through the telescope,
you’ll see it drift slowly across the eld of view. To keep it in
the eld, assuming the equatorial mount is polar aligned, just
turn the R.A. slow-motion control cable counterclockwise to
track. The Dec. slow-motion control cable is not needed for
tracking. Objects will appear to move faster at higher magni-
cations, because the eld of view is narrower.
Optional Electronic Drive for Automatic Tracking
An optional DC electronic drive is available for the EQM-13
equatorial mount. This battery-operated drive provides auto-
mated, hands-free tracking. Objects will then remain station-
ary in the eld of view without any manual adjustment of the
R.A. slow-motion control cable.
Understanding the Setting Circles
The two setting circles on an equatorial mount enable you to
locate celestial objects by their “celestial coordinates”. Every
object resides in a specic 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 online planetarium app.
On the EQ-13 mount, the R.A. setting circle is scaled in hours,
from 1 through 24, with small marks in between representing
10-minute increments (Figure 11). The numbers at the base
of the setting circle scale apply to the Northern Hemisphere
while the numbers above them apply to viewing in the
Southern Hemisphere.
The Dec. setting circle is denoted in degrees, with each main
mark representing 10° increments (Figure 11). Values of Dec.
coordinates range from +90° to -90°. The 0° mark indicates
the celestial equator. For this mount, the number scale goes
to 90 on either side of 0 – there are no (+) or (-) signs. When
the telescope is pointed north of the equator, actual values of
Dec. are negative.
For example, the coordinates for the Orion Nebula (M42) are:
R.A. 5 hr 35.4 min, 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 polar aligned, and the setting circles must be
calibrated. The easiest way to calibrate the setting circles is
to point the telescope at an identiable bright star, center it
in the eyepiece, then set the setting circles to the star’s pub-
lished coordinates, which you can nd in a star atlas or astro-
nomical software program, or perhaps on the internet.
Calibrating the Setting Circles
Using a star atlas or astronomy planetarium program, identify
a bright star visible in your sky. Some smartphone astronomy
apps allow you to hold your phone up to the sky and the app
will identify the stars and constellations visible in the direction
you’re pointing to. Note the right ascension and declination
coordinates of the star.
Let’s take as an example Altair, in the constellation Aquila. Its
coordinates are:
R.A. 19 hr 51 min, Dec 8° 52'
1. Loosen the R.A. and Dec. lock knobs on the equatorial
mount, so the telescope optical tube can move freely.
2. Point the telescope at Altair. Lock the R.A. and Dec. lock
knobs. Center the star in the eyepiece with the slow-motion
control cables.
3. Rotate the R.A. setting circle until the metal arrow indicates
19 hr 51 min.
4. Then rotate the Dec. setting circle until the metal arrow indi-
cates +8° 52'
Note that the setting circles may be a little hard to rotate.
But just grab it rmly around the edge and twist it and it
will rotate.
Finding Objects with the Setting Circles
Now that both setting circles are calibrated, look up the coordi-
nates of an object you wish to view.
1. 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 if you’re in the Northern
hemisphere. Retighten the lock knob.
2. 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 equa-
tor. 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 or near the eld of view of the
nder scope, assuming the equatorial mount is accurately
polar aligned. Use the slow-motion controls to center the object
in the nder scope, and it should appear in the telescope’s eld
of view.
The R.A. setting circle must be re-calibrated 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. One
thing you DO NOT do is make any adjustment to the mount’s
latitude setting or to its azimuth position. That will throw off the
mount’s polar alignment. Once the mount is polar aligned, the
telescope should be moved only about the R.A. and Dec. axes.
This is done by loosening one or both of the R.A. and Dec.
lock knobs and moving the telescope by hand, or keeping the
knobs tightened and moving the telescope using the slow-
motion cables.
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