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.
The table above provides the dates and concise data to hunt for the youngest possible lunar crescent in this country, which is a very challenging activity.
First sighting of the new crescent moon is used as the basis of various calendars to signal the start of the new month. For instance, Islam requires that the sighting of the the new crescent moon should be made with the naked eye.
Predicting the first sighting of the new crescent moon has been attempted since the time of the Babylonians. These ancient methods relied on the age of the Moon and the time difference between moonset and sunset. More modern methods use the angular separation of the Sun and Moon, the altitude difference between the Sun and Moon, their relative azimuths and the width of the crescent.
The following table shows the dates of possible first sighting of new moon crescent (in Arabic known as hilal) for Brunei Darussalam. These dates are colour-coded based on the moon altitude and a crude prediction of the new moon sighting can be related as follow:
1. Red that indicates the moon altitude which is less than 2°. A very slim chance of visibility due to low altitude.
2. Orange that signifies the moon altitude between 2° and 5.5°. There is a slim chance of crescent visibility. However visibility might be improved with the use of optical aids and excellent atmospheric conditions.
3. Yellow that the moon is at altitude between 5.5° and 7.5°. There is a good chance that the crescent is visible to the naked eyes under excellent atmospheric conditions.
4. Green that shows the moon’s altitude is more than 7.5°. The lunar crescent is positioned reasonably high above the horizon making it easily visible to the naked eye.
If you manage to sight the crescent on the dates provided, please share your experience and photos via firstname.lastname@example.org
Buku ini adalah dihasratkan sebagai rujukan bagi ilmuan-ilmuan di Negara Brunei Darussalam dan sumbangan kajian berunsur saintifik. Di dalam buku ini terkandung kompilasi jadual waktu bagi kenampakan anak bulan yang pertama. Penghasilan jadual ialah dengan mengunakan berbagai-bagai perisian astronomi dan program yang diaturacara oleh Hazarry bin Hj Ali Ahmad.