Instruction manual
14
The Index Marker
The polar scope in combination with the RA setting circle
constitutes a circular slide rule. This slide rule is used to
calculate the hour angle of Polaris at your local time
anywhere on the planet. On a given day of the year, eg
March 30, at a given local time, eg 10:00pm, the hour
angle of Polaris is the same, anywhere on the planet.
This is an approximation, which is good to about 4
minutes of arc. The index marker represents a 'zero' for
the slide rule. If the zero is not set correctly, the
calculated hour angle will not be correct.
Unlock the RA locking knob. Rotate the telescope around
the RA axis so the reticule is as shown in Fig g-10. Re-
tighten the RA locking knob to lock the RA axis in this
position. In this position, Polaris is in transit - it is at its
highest point in the sky.
Unlock the RA setting circle by loosening the set screw.
Rotate the RA Circle so the pointer indicates 'zero' and
lock the RA Circle. This sets the first of two 'zeros'
required for the slide rule. Now rotate the telescope
around RA axis so the RA Circle indicates 1h 0m (Fig.g-
11). Lock the RA axis. Rotate the Date circle so October
10 is indicated (see Fig.g-11 for HEQ5, Fig.g-12 for EQ6
). At 1:00 AM local time, on October 10, Polaris is in
transit anywhere in the world. Rotate the telescope
around the RA axis so the RA circle indicates 'zero' and
lock the RA axis. The view through the Pole Finder
should be the same as before.
Loosen the setscrew on the index marker ring. Adjust the
index marker ring so the Date circle reads 'zero' on the
longitude indication (Fig.g-13). Secure the ring by
tightening the setscrew. This sets the second of the two
zero points.
If the reticule has been re-aligned or the index ring has
come loose, this procedure must be carried out again to
ensure accurate polar alignment.
P
olar
i
s
NC
P
O
c
t
a
n
s
C
a
s
s
i
o
p
e
i
a
B
i
g
D
i
p
p
e
r
Make this line
vertical
Place this circle
on the bottom
(diagram applicable to both mounts)
10
11
12
9
8
Set screw
Rotate this ring
Index mark
should be here
EQ6
0
2
2
2
2
3
1
2
1
20
23
3
1
2
1
4
3
1
9
2
1
5
1
8
6
Pointer
RA setting circle
Set screw
RA Locking knob
HEQ5
Date circle
10
1
1
9
8
RA setting circle
0
1
22
2
3
23
23
1
22
2
3
21
4
5
1
9
Set screw
Pointer
10
1
1
9
8
Fig.g-10
Fig.g-11
Fig.g-12
Fig.g-13