INTERNATIONAL OCCULTATION TIMING ASSOCIATION

The International Occultation Timing Association (IOTA) was established to encourage and facilitate the observation of occultations and eclipses.

Accurate time signals are needed for timing occultations. The time provided by the telephone company in most North American cities is not accurate enough; you should not use it. In the U.S.A., accurate time signals, from the U. S. Naval Observatory master clock, can be obtained by calling 900-410-8463; the call should be placed via AT&T to ensure use of land lines, which will give an accuracy of a few hundredths of a second, more than sufficient for visual timings.

Most observers find stopwatches most convenient for making timings. Unfortunately, most stopwatches now are digital. Stopwatches with dial displays (such as those on most mechanical stopwatches) are needed for some of the timing methods discussed in Van Flandern's Precision Timing of Occultations (P.T.O.). Methods that don't use a stopwatch include the Eye-and-Ear method and tape recording method, discussed in P.T.O. If a tape recorder is used, total occultation times should be marked with a mechanical clicker (such as a toy cricket) or buzzer (such as for a door bell) rather than with voiced calls. Voiced calls are sufficient for grazing occultations, where half-second timings are acceptable.

For reporting occultations, you need to determine your accurate geographical longitude, latitude, and height above sealevel. These can be measured from a large-scale topographic map of your area, preferably with a scale in the range of 1:50,000 to 1:24,000. Check your telephone book for map, engineering supply, or sporting goods stores in your area that sell these maps. College, University, and sometimes municipal libraries have map collections that you might be able to use to measure positions.

Timing and reporting occultation events with a camcorder

We want to be able to determine the accurate times of the disappearance (D) and/or the appearance (R) of the star from behind the Moon. You just need to record for 2 to 3 minutes around the D and R events. If you have a receiver for WWV shortwave time signals at 5.0 and 10.0 megahertz, record them while you make the observation, including at least 3 minute marks around each event. 5 and 10 megahertz are the best night frequencies (10 best in twilight conditions); 15.0 megahertz is usually needed in the daytime. Digital shortwave radioes that can receive WWV can be purchased for about $100 from electronics stores such as Radio Shack; a 50-foot copper wire attached to the antenna can improve reception. If you don't have WWV, then record the Cable News Network (CNN; it is easier to use than the previously-used Weather Channel since CNN has much less local broadcasting) for about a minute starting 4 or 5 minutes before the event time, then go outside with the camcorder still recording to be ready for the D or R 2 minutes before the expected time. After the event happens (if it was recorded), go back inside with the camcorder still running, and record more of CNN for 1 to 2 minutes. If your camcorder has a running time display with seconds, keep it running the whole time. It does not need to be set accurately since we will precisely calibrate it with the CNN broadcast that you have recorded before and after the event. You do not need to keep the camcorder running through the whole occultation. But be sure that you have several minutes of tape, enough to record everything for the event, and if you have a telescope, enough for both the D and R as well.

*** IMPORTANT *** If you record CNN, we need to know whether it was received by cable from a local Cable TV company, or if it was received with a satellite dish (direct satellite broadcast). If you have receivers for both WWV and CNN, please record some of both together before and after the occultation, and preferably for several minutes; they will help us calibrate the more numerous CNN only tapes made in your area.

THANKS. This is a long-term project that will take a few years to achieve its goal of providing accurate measurements of the edge of the Moon. These are mainly needed for the proper analysis of past solar eclipse timings, which in turn are used to determine small but climatically significant cyclical variations of the Sun's diameter. We greatly appreciate your contribution to this effort.

David Dunham, President, 1997 August 29 International Occultation Timing Association 7006 Megan Lane Phone: 301-474-4722 Greenbelt, MD 20770-3012 Weekdays: 301-953-5609 Email: Joan and David Dunham