630315Eclipse3_p3

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Eclipse Bulletin No. 3 cont'd.

PRECISION OBSEVATIONS

1. DURATION OF TOTALITY

    This is a straightforward observation that can be performed, without optical
equipment, by junior members or by members who feel that they lack the experience
to undertake anything more difficult.  It can be developed into a project in which
the general public can participate, as will be described in a later bulletin. For
this observation we are not interested in the time at which totality occurs but
simply in the length of the period of totality. This should be timed, as accurately
as possible, using an ordinary watch with a second hand or a short-wave radio (see
timing methods (1) and (2) or a stopwatch.



2. TIMING OF CONTACTS

    The main purpose for the accurate timing of the eclipse has been to determine
geodetic positions. While it is true that more accurate results can now be obtained
using satellite orbits, the timing of contacts is nevertheless of considerable
interest. The beginning and end of totality (2nd and 3rd contacts) are very defin-
ite and can be observed without optical aid. They should be timed with great acc-
uracy, to the split second if possible. If Timing Method (3) is used, two stop-
watches are needed, for there will not be time between contacts to check the watch
to time signals and have it ready for use again. Telescopes are needed to observe
the 1st and 4th contacts (the first and last contacts of the moon's disk with that
of the sun) which are very indefinite and cannot be timed with the same accuracy.
It might be better to reserve the telescopes for other work or possibly combine
timing of 1st and 4th contacts with observation of the occultation of sun-spots,
which is described below.



3. OCCULTATION OF SUN-SPOTS

    The purpose of this project is to make available accurate timings of occultation
of sun-spots for correlation with radio observations of the sun made during the
eclipse. Preferably, the project should be undertaken by art experienced solar
observer, using a telescope equipped with a Herschel wedge, etc. or a projection
screen. The observer makes a regular solar observation earlier in the day, record-
ing the usual data, plotting on a disk the positions of all sun-spot groups and
ù assigning a number to each for ready reference in the eclipse report. During the
eclipse, between first bontact andthe beginning of totality, the observer clocks
the time at which each sun-spot. group is occulted by the moon.  If it is a large
group, contacts with both preceding and following edges should be clocked.  If it
is a small group, the time at which it is bisected should be clocked.  Although we
are going through a period of minimum solar activity, let us hope that there are
some conspicuous spots on the sunts disk that day. If there are a number, then
Timing Method (3) would not be practi¢al because of the number of stopwatches
required. Occultations need be timed only to the nearest second and therefore any
of the other three timing methods can be used. The occultation reappearance of
the sun-spots can be clocked, too, of course.


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