Annexure E National Mapping specifications for Sigma Octantis Azimuth Observation
(Extract from Specifications for second order tellurometer traversing, May 1967,
pages 11-13)
5. 2nd Order Sigma Octantis Azimuths using WILD T3 and T2 Theodolites.
5.1 Main equipment necessary:
1. WILD T3 or T2 Theodolite and lightning set.
2. Radio capable of receiving W.W.V. or Lyndhurst - preferably a small transistor radio.
3. Split hand stop watch.
4. Pocket watch with second hand.
5. Observing screen or tent. (not used at Ayers Rock observation)
6. Small table and booking lamp. (table not used at Ayers Rock observation)
7. Torch for reading plate bubble and stop watch.
8. Lucas lamp and time switch. (not used at Ayers Rock observation)
5.2 Time of Observation:
Observation will be commenced immediately after sunset or as soon as Sigma Octantis is visible.
This is the most accurate period in which to observe as the R.O. light is usually at its steadiest at
this time.
5.3 Reference Object:
A Lucas lamp or other suitable light will be used. It is important, particularly on low lines, to keep the
lamp as high above the ground a possible. The lamp will be plumbed over the station mark or placed
exactly on line.
5.4 Stand Point:
The same care will be taken with the stand point as for horizontal angles.
5.5 General Preparations:
1. The altitude and azimuth of Sigma Octantis to the nearest 2' of arc is calculated for the approximate
start time of the observation. This is best done by means of a suitable graph. (supplied by
National Mapping). Before looking up the graph it is necessary to calculate the L.S.T. (Local Sidereal
Time) at which it is desired to commence observing.
2. The pocket watch will be set approximately 10 secs. fast on standard time.
3. The stop watch will be started at a suitable time, i.e
if a 30 min. dial at 00 or 30 mins.,
if a 15 min. dial at 00, 15, 30, or 45 mins.
It will be started, within 1 or 2 seconds, to the same reading as the pocket watch. This means, that
both watches are approximately 10 secs. fast on standard time and therefore any errors are more
easily detected.
4. The stop watch will be compared to Lyndhurst, W.W.V. or W.W.V.H. time signal, noting the error
to the nearest 1/10th second just prior to commencement of azimuth observations and also
after every three double arcs, thus. - at the commencement, after the third double arc, and after the
sixth double arc.
(The time signal at Ayers Rock was W.W.V.H. on SW2, 9.00 Mhz exactly)
5.7 Point to Point Description of Actual Observing Method on WILD T2 and T3.
After checking that the instrument has been levelled, parallax and focusing adjusted, and the lighting in
the telescope and scales checked, then:
1. Take to pointings and two micrometer readings on R.O. light in the same manner as for horizontal
angles.
2. Set on altitude and azimuth of the star as called out by the booker.
3. Intersect star with single vertical wire and call "up", at the same time pressing the stop watch button.
Booker at this point records the coarse time from the pocket watch to the nearest second.
4. Call out the stop watch reading and the plate bubble readings, East and West, in that order.
5. Bring scales into coincidence and read off the horizontal angle.
6. Take a fresh pointing and micrometer reading, again reading the stop watch and the plate bubble.
7. A vertical circle reading will now be taken to the star.
8. Change face on the star. The booker will call out the vertical and horizontal settings if desired by the
observer.
9. Take two more pointings, bubble readings, etc., on the star as before.
10. Swing back on the R.O. light and take two pointings and micrometer readings. This completes one
double arc.
11. Re-level the instrument carefully before commencing the next double arc.
Fig. E1 Diagram illustrating the position of Sigma Octantis with
respect to adjacent stars as seen in the field of view of
the telescope of a T2 theodolite.