By MOHAMMAD SH. ODEH, Arab Union for Astronomy and Space Sciences (AUASS), P.O. Box 141568, Amman 11814, Jordan (e-mail: email@example.com) (Received 12 May 2005; accepted 19 September 2005)
Abstract. A new criterion for lunar crescent visibility has been established using 737 observations, almost half of them obtained by the Islamic Crescent Observation Project (ICOP). This criterion is based on two variables, viz. the topocentric arc of vision and the topocentric crescent width. The new model is able to predict the visibility of the lunar crescent both for naked eye and optically aided observations. From the database we found a Danjon limit of 6.4 degrees.
Introduction The lunar crescent visibility has been studied by many astronomers since the Babylonian era, with as a result currently more than 12 different criteria for lunar crescent visibility, based on a number of sightings in different lunar conditions. Many of these criteria were developed by Islamic astronomers, since a number of Islamic religiouseventsaredirectlyrelatedtolunarcrescentsighting.Forexample,thenew Lunar (Hijric) month begins on the next day of sighting the new crescent at west after sunset.
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