Dorr DANUBIA ATLAS 2000 Bedienungsanleitung Seite 22

07.11 USING THE SETTING CIRCLES
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 repre-
senting 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 coordi-
nates. 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.
08 | USING THE POLARSCOPE (OPTIONAL)
The Polar Alignment Finderscope or 'polarscope' gives Northern Hemisphere users a convenient tool for
pointing at the NCP. It has a large circle circumscribing the path of Polaris, with the NCP located at the cross-
hair, and it has a smaller circle to indicate the direction of Polaris. However, the Earth rotates and the orienta-
tion of the stars changes, so a method is needed to obtain the correct alignment of Polaris in the polarscope,
for the date and time of your viewing session.
Aligning the polarscope to the mount´s polar axis
This is most easily done by pointing at a terrestrial target with the RA drive turned off. To allow full rotation
around the RA axis, remove the telescope and the counterweight, including the rod. Unlock the DEC. clutch
and rotate to Dec 0°, then lock the DEC. clutch. Remove the cap from the bottom of the RA axis shaft and the
plug from the top (Fig.k, EQ5 shown here).
At the bottom of the polar shaft is a black, 24-hour clock dial. The top row of numbers is for Northern Hemis-
phere use, the lower for the Southern Hemisphere. Unlock the setscrew just above it and rotate the dial until
zero is aligned with the indicator cast into the metal just below the screw. Tighten the setscrew to lock the
dial (Fig.k1). The silver dial just below it is a calendar dial. The months are numbered 1-12. The longest lines
separate the months, the middle-length lines are ten days apart, and the short lines between them are two
days apart. The black collar holding this silver dial in place, has an indicator line inscribed on it. The numbers
nearest this collar are marked "E 20 10 0 10 20 W". These will be explained later, but for now rotate the silver
dial until the middle zero is aligned with the indicator line on the black collar. At midnight on November 1, on
the Central Meridian of your local time zone, Polaris is directly above the NCP. It is therefore directly below
when viewed through the inverted view of the polarscope. This provides a good way to orient the polarscope
in the mount.
Fig.j
Fig.k
DEC. lock knob
Fig.k1
22
1 minute
+
8 hours and 20 minutes
(Northern Hemisphere)
=
8 hours and 21 minutes
15 hours 40 minutes
–
1 minute
=
15 hours and 39 minutes
(Southern Hemisphere)
R.A. lock knob
DEC. scale
Setscrew
Indicator
24 hour clock
Date circle
Meridian Offset
Indicator
Polarscope holder
Polarscope-
alignement screw
Polarscope
Setscrew
Pointer
R.A. Setting Circle
Date circle
Polarscope holder
Polarscope
alignment screw