ORION TELESCOPES & BINOCULARS 52588, Instruction Manual

10

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.

Understanding the Setting Circles

The two setting circles (

Figure 7) on an equatorial mount 

enable you to locate celestial objects by their “celestial coordi-
nates”. Every object resides in a specific location on the “celestial 
sphere”. That location is denoted by two numbers: its right ascen-
sion (R.A.) and declination (Dec.). In the same way, every loca-
tion 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 mount’s R.A. setting circle is scaled in hours, from 1 through 
24, with small marks in between representing 10-minute incre-
ments. The numbers closest to the R.A. axis gear apply to view-
ing in the Southern Hemisphere, while the numbers above them 
apply to viewing in the Northern Hemisphere. 
The Dec. setting circle is scaled in degrees, with each mark rep-
resenting 2.5° 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, while 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 are:
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-min-
utes in 1 degree of declination). 
Before you can use the setting circles to locate objects, the 
mount must be properly polar aligned, and the R.A. setting circle 
must be calibrated. The Dec. setting circle has been permanently 
calibrated at the factory, and should read 90° whenever the tele-
scope optical tube is parallel with the R.A. axis. 

Calibrating the Right Ascension Setting Circle

1.  Identify a bright star in the sky 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 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.  Rotate the setting circle until the metal arrow indicates the 

R.A. coordinate listed in the star atlas for the object. 

Finding Objects with the Setting Circles

1.  Now that both setting circles are calibrated, look up in a 

star atlas the coordinates of an object you wish to view.

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 upper set 
of numbers on the R.A. setting circle. Retighten the lock 
knob.

3.  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 the field of view of the red dot 
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 telescope’s field 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 (don’t touch the azimuth lock 
knob). 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 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. 

5. Astronomical Observing

For many, this will be your first foray into the exciting world of 
amateur astronomy. The following information and observing 
tips will help get you started.

Choosing an Observing Site

When selecting a location for observing, get as far away as pos-
sible from direct artificial light such as street lights, porch lights, 
and automobile headlights. The glare from these lights will great-
ly impair your dark-adapted night vision. Set up on a grass or 
dirt surface, not asphalt, because asphalt radiates more heat. 
Heat disturbs the surrounding air and degrades the images seen