9
Using the Vernier Scale
The R.A. setting circle includes a Vernier scale (Figure 3d) in
order to read fractions of ticks on the R.A. circle. The smallest
marks on the R.A. scale are 10 minutes of arc, and the Venier
scale divides each of these marks into 10, meaning you can get
a resolution of 1 arc minute when using the Vernier scale.
Look at the Venier scale and notice how the lines almost match
up with tick marks directly below it on the R.A. scale. They almost
match up, but not quite. Count from the 0 on the Venier scale
until you reach a R.A. mark that lines up because it is DIRECTLY
below a mark on the Venier scale. That corresponding number
on the Venier scale is the number of arc minutes between the
two R.A. marks under the main R.A. pointer. So for example, if
you R.A. pointer is sitting between the 12h 10min mark and the
12h 20min mark, and the 3rd mark on the Venier scale lines up
with a mark below it, that means the scope is pointing to 12h
13minutes of R.A.
Confused About Pointing the Telescope?
Beginners occasionally experience some confusion about
how to point the telescope overhead or in other directions. In
Figure 1
the telescope is pointed north as it would be dur-
ing polar alignment. The counterweight shaft is oriented down-
ward. But it will not look like that when the telescope is pointed
in other directions. Let’s say you want to view an object that is
directly overhead, at the zenith. How do you do it?
DO NOT make any adjustment to the latitude adjustment
T-bolts. That will spoil the mount’s polar alignment. Remember,
once the mount is polar aligned, the telescope should be moved
only on the R.A. and Dec. axes. To point the scope overhead,
first loosen the R.A. lock lever and rotate the telescope on the
R.A. axis until the counterweight shaft is horizontal (parallel to
the ground). Then loosen the Dec. lock lever and rotate the
telescope until it is pointing straight overhead. The counter-
weight shaft is still horizontal. Then retighten both lock levers.
What if you need to aim the telescope directly north,
but at an object that is nearer to the horizon than
Polaris? You can’t do it with the counterweights down
as pictured in
Figure 1
. Again, you have to rotate
the scope in R.A. so that the counterweight shaft is
positioned horizontally. Then rotate the scope in Dec.
so it points to where you want it near the horizon.
To point the telescope directly south, the counterweight shaft
should again be horizontal. Then you simply rotate the scope
on the Dec. axis until it points in the south direction.
To point the telescope to the east or west, or in other directions,
you rotate the telescope on its R.A. and Dec. axes. Depending
on the altitude of the object you want to observe, the counter-
weight shaft will be oriented somewhere between vertical and
horizontal.
Figure 8
illustrates how the telescope will look when pointed
at the four cardinal directions: north, south, east and west.
The key things to remember when pointing the telescope are
that a) you only move it in R.A. and Dec., not in azimuth or
latitude (altitude), and b) the counterweight and shaft will not
always appear as it does in
Figure 1
. In fact it almost never
will!
7. Specifications
Mount:
German equatorial
Tripod:
Aluminum, adjustable height,
accessory tray included
Counterweights:
7lbs. 9oz. and 4lbs.
Slow-motion controls:
For both R.A. and Dec. axes
Setting circles:
R.A. scaled in 10 min. increments,
Dec. scaled in 2° increments.
for N or S Hemispheres
Latitude adjustment:
5° to 75°
Polar Alignment:
Polar scope with N hemisphere
reticle included
Motor drives:
Optional
Weight:
27.5 lbs.
Polar Alignment:
Polar axis finder scope for
Northern Hemisphere included,
fine adjustments for latitude and
azimuth
Figure 8.
This illustration shows the telescope pointed in the four cardinal directions:
(a)
North,
(b)
South,
(c)
East,
(d)
West. Note that the
tripod and mount have not been moved; only the telescope tube has move on the R.A. and Dec. axis.
8a
b
c
d