Note: If you have an optional motor drive attached, you will need to loosen the clutch on the R.A. (and Dec. for
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.
Optional Motor Drives for Automatic Tracking
An optional DC motor drive can be mounted on the R.A. axis of the equatorial mount to provide
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 loca- tion on Earth can be described by its longitude and latitude. Right ascension is similar to longitude on Earth, and declina- tion 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
The Dec. setting circle is scaled in degrees, with each mark representing 2° increments. Values of declination coordinates range from +90° to
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
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.
Calibrating the Declination Setting Circle
1.Loosen the Dec. lock lever and position the telescope as accurately as possible in declination so it is parallel to the R.A. axis as shown in Figure 1.
2.Loosen one of the thumbscrews on the Dec. setting circle (see Figure 12), this will allow the setting circle to rotate freely. Rotate the Dec. setting circle until the pointer reads exactly 90º.
Calibrating the Right Ascension Setting Circle
1.Identify a bright star in the sky near the celestial equator (declination = 0°) 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. Lock the R.A. and Dec. lock levers. Center the star in the telescope’s field of view with the
4.Loosen one of the R.A. setting circle thumbscrews (see Figure 12); this will allow the setting circle to rotate freely. Rotate the setting circle until the R.A. pointer arrow indi- cates the R.A. coordinate listed in the star atlas for the object.
Dec. setting 
circle
Dec. set- |
| R.A. setting |
ting circle |
| circle |
| ||
thumbscrew |
|
|
(2) |
|
|
Dec. indicator arrow
R.A. indicator 
arrow
R.A. setting circle thumbscrew (2)
Figure 12. The R.A. and Dec. setting circles.
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.
Loosen the Dec. lock lever and rotate the telescope until the declination value from the star atlas matches the reading on the Dec. setting circle. Remember that values of the Dec. set- ting 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 lever.
Loosen the R.A. lock lever and rotate the telescope until the right ascension 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 lever.
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