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Session 1 - HAD I: LeRoy E. Doggett Memorial Session.
Oral session, Tuesday, January 06
Georgetown,
Historically, many calendars are based on lunar months, where the start of the month is based on the sighting of the thin crescent Moon in the evening twilight. Yet the problem of predicting (or postdicting) crescent visibility is a difficult task. In modern times, the Islamic calendar is used by more than a billion people, while its utility is abridged by the ambiguities in knowing the dates. As such, I would claim that crescent visibility is the single (nontrivial) astronomical problem that affects the most people. LeRoy Doggett spearheaded an effort to place crescent visibility on a firm observational basis by organizing five Moonwatch campaigns involving thousands of observers spread out across North America. His idea was to collect large numbers of actual observations for direct confrontation with models, and to measure the error rates. This talk will report on his results. The application of the results are broad; frequently in areas of scholarly, historical, social, or military disputes. For example, lunar visibility is vital for dating the Crucifixion, a task contentious among Biblical scholars. Another example is in testing the historicity of the claimed lunar impact reported by Gervase of Canterbury. The meeting will be held in the middle of the Islamic holy month of Ramadan, while in the past two decades the majority of Ramadans have been started based on reported crescent sightings before the time of New Moon.
