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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. - 3 -