Introduction
We set up at a site
near the northern limit to observe Baily's beads to provide data for
the determination of Solar radius variations for Alan Fiala of the
USNO.
Our site was a
beautiful beach near Sungailiat, Bangka Island know as Pantai Matras,
illustrated in Figure 1, but the actual
observations were conducted at Pantai Tengarri near Point
Lajang.
The position of the
site determined from 1:50,000 maps, was 01 degree 48 minutes 16.9
seconds South, 106 degrees 7 minutes 34.5 seconds East, with our
observing sites at sea level. The longitude is in doubt as the 1969
UK Ministry of Defence 1:250,000 scale maps of the island scaled to a
value of 106d 7m 15s.
Observations were
made by direct viewing through full aperture solar filters of single
coated aluminised Mylar. The cloudy conditions just before first
contact prevented use of planned eyepiece projection techniques from
our 40 mm refractors.
Many successful
timings were made and from the recorded time of totality of 48.2
seconds it is estimated that we were placed only 4.4 km inside the
predicted northern limit, at 94 per cent of the path width from the
centre line.
Observation
timings
A tape recorder was
used and by numerous playbacks, event timings were obtained using a
Hewlett-Packard time module for split timings. The taped dialogue,
timing base and split timings obtained are shown in
Table
1 with the UT of each event corrected for a tape recorder
drift.
Instrumentation
I used a full
aperture solar filter on a 40 mm UNITRON reflector with a 12.5 mm
eyepiece on a small photographic tripod with a FM/AM PLL synthesised
radio receiver, memory preset for time seeking from mainly WWV and
two tape-recorders for dialogue and radio signals placed near each
other. Cathie used a make-shift half aperture solar
filter on a poorer quality 30X40 mm Martinscope refractor mounted on
a camera tripod.
The primary tape
recorder microphone failed just before first contact, but as both of
our sites were adjacent (due to our inability to obtain eyepiece
projected images through the initial heavy cloud) my comments were
fortunately recorded on Cathie's
tape. The low comments
given in Table 1 were not expletives, but those intended for the
failed tape recorder.
Some minor events
may have been missed but the majority were recorded as explained.
Weather conditions
were fine, but with some cirrus cloud during the beginning of the
event. Many spectators
were present on the beach but all were well behaved, some spoke to us
in fine English particularly after the eclipse was
over. Some other photos were taken, one is shown of
Point Lajang in Figure 2, while
Figure 3 and Figure
4 illustrate the site conditions just before the eclipse.
Conclusions
On page 24 of USNO
Circular No. 172, March 1987, the predicted time of totality at
Sungailiat (location 106d 06.5m E, 1d 51.5m S) is given as 1m 18.8s
at 0h 32m 38.1s with a total path width of 147km.
Our time of
totality was reduced to 48.2s and was observed at a mid-time of 0h
32m 38.2s.
Hence, as reported
for our second solar eclipse expedition to Papua New Guinea in 1984
(2), the observed time of totality allows a calculation of our
position in terms of distance from the centre line by using the
expression:
t = t p (1 - (x)
2)0.5 where x is the site/path width
ratio
and t p is the predicted time of
totality at the centre line.
As we observed
about 5km north of Sungailiat to optimise the number of Baily's
Beads, where the above expression gives an estimated distance ratio
for our sites of 94% from the centre line of the path, based on the
USNO circular predictions for the time of totality of 2m 25.9s near
the longitude of Sungailiat.
The large number of
beads recorded are (hopefully) supplemented by those timings made
near (but not as close as planned) the southern limit. See Herald and James report
(3).
Others of our
expedition were successful with brightness and temperature
measurements and general photographic observations, see Tregaskis
Report (4).
Acknowledgements
Many thanks are due
to Koba Tin Management and Staff for their hospitality at their very
comfortable Mining Camp and to the inhabitants of the unspoilt island
of Bangka, and to the ever courteous Indonesian Government
officials.
References
(1)
Fiala, A.D., et al, Bull.American Astron. Soc. 624, 17(2),
1985.
(2)
Soulsby, B.W., Australian Journal of Astronomy Vol.1 No.1.
10-26, April 1986.
(3)
Herald, D.R., James, A, to be published.
(4)
Tregaskis, T.B., private communication, 25 April,
1988.
