Using The Setting Circles - SKY-WATCHER S11670 User Manual

The quickest way to find objects is to learn the Constellations
and use the finderscope, but if the object is too faint you may
want to use setting circles on an equatorial mount. Setting
circles enable you to locate celestial objects whose celestial
co-ordinates have been determined from star charts. Your
telescope must be Polar aligned and the R.A. setting circle
must be calibrated before using the setting circles.
Reading the R.A. setting circle
The telescope's R.A. setting circle is scaled in hours, from 1
through 24, with small lines in between representing 10
minute 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 section next to the set crew is scaled in minutes, from 1
through 10, representing the exact minute within the 10
minute increments.
In the case of Fig.j, the R.A. setting circle pointer indicates
approximately 8 hours and 20 minutes. Now look for the
number in the minute scale that aligns with any line on the
main R.A. setting circle. In this case, it is 1. The reading on
this R.A. setting circle, therefore, is 8 hours and 21 minutes.
Setting (calibrating) the R.A. setting circle
In order to set your Right Ascension circle you must first find
a star in your field of view with known coordinates. A good
one would be the 0.0 magnitude star Vega in the
Constellation Lyra. From a star chart we know the R.A.
coordinate of Vega is 18h 36m. Loosen the R.A. and DEC.
lock knobs on the mount and adjust the telescope so that
Vega is centred in the field of view of the eyepiece. Tighten
the R.A. and DEC. lock knobs to lock the mount in place.
Now rotate the R.A. setting circle until it reads 18h36m. You
are now ready to use the setting circles to find objects in the
sky.
Finding objects using the setting circles
Example: Finding the faint planetary nebula M57; "The Ring"
From a star chart, we know the coordinates of the Ring are Dec. 33º and R.A. 18h52m. Unlock the DEC lock knob
and rotate your telescope in DEC until the pointer on the DEC setting circle reads 33º. Re-tighten the DEC lock
knob. Loosen the R.A. lock knob and rotate the telescope in R.A. until the pointer on the R.A. setting circle reads
18h52m (do not move the R.A. circle). Re-tighten the R.A. lock knob. Now look through the Red Dot Finder to see
if you have found M57. Adjust the telescope with R.A. and DEC. flexible cables until M57 is centred in the Red
Dot Finder. Now look through the telescope using a low power eyepiece. Centre M57 in the field of view of the
eyepiece.
If you are familiar with the night sky, it is sometimes convenient to find an object using only the DEC coordinate.
Loosen the DEC. lock knob and rotate the telescope in DEC. until the pointer on the DEC setting circle reads 33º.
Re-tighten the DEC. lock knob. Now traverse through Lyra in R.A. axis until M57 appeares in the field of view.
The setting circles will get you close to the object you wish to observe, but are not accurate enough to put it in the
centre of your Red Dot Finder's field of view. The accuracy of your setting circles also depends on how accurate
your telescope is polar aligned.
14
Setscrew
Pointer
R.A. Setting Circle
Date circle
Polarscope holder
Polarscope
alignment screw
Fig.j
1 minute
+
8 hours and 20 minutes
(Northern Hemisphere)
8 hours and 21 minutes
15 hours and 40 minutes
-
1 minute
15 hours and 39 minutes
(Southern Hemisphere)