Analysis of Observations of Earliest Visibility of the Lunar Crescent By Dr Thamer Alrefay (et al)
National Center for Astronomy, KACST, Riyadh, Saudi Arabia
"Predicting the visibility of thin lunar crescents following the new moon is difficult and challenging for several technical reasons. The visibility of the earliest new moon has long been used to determine the lunar-crescent calendar and is still used today. Many criteria exist for the first visibility of the lunar crescent. Here, we test the most-commonly-used criteria for thin-lunar-crescent visibility. We used 545 observations, including both positive and negative sightings, made by professional and highly-trained astronomers over a duration of 27 years (1988 - 2015) and from different locations at latitudes between 20° N and 29° N (within Saudi Arabia). We developed a new criterion for lunar-crescent visibility using lunar-crescent width (W) and the arc of vision (ARCV). This new model can be used to predict the visibility of the lunar crescent by the naked eye or aided eye, which is fundamental for the lunar-crescent calendar followed by several cultures and religions." [Read more] | Ref: The Observatory Journal, Vol. 138, No. 1267, December 2018
Frequently Asked Questions
| Question: | Why did it take so long to publish this paper (27 years)? |
| Answer: | It took a long time because: (a) they needed a large collection of data for accuracy of statistical analysis; (b) they needed data from all seasons, including dusty summer and clear winter times, positive & negative results; (c) they wanted high accuracy of data, so they only accepted observation reports from experienced observers who recorded the details accurately/immediately after the observation. |
| Question: | How were the crescent observers highly-trained? |
| Answer: | They were highly-trained observers because most of them have postgraduate qualifications in an astronomy related subject and/or have been undertaking monthly crescent moon watch for many years with other experienced observers. As an example of their credentials, the author (Dr Thamer Alrefay) holds the following qualifications: (a) PhD in Space Physics (University of New Brunswick, 2014); (b) MSc in Space Science (Florida Institute of Technology, 2003); (c) BSc in Astrophysics (King Abdulaziz University, 1996) |
| Question: | How does this research comply with the Islamic law of worship (Ibadah)? |
| Answer: | This research finding is based on actual observations by the human eye (i.e. in visible-light wavelength and not in infra-red/CCD imaging wavelength). It was conducted by a large number of people so constitutes average eyesight observations within Saudi Arabia (20° N to 29° N latitude). Therefore, it is most suitable for improved civil calendar criteria for Saudi Arabia, which will match with actual moon sighting for all Islamic lunar months (e.g. start and end of Ramadan), InShaAllah. |
| Question: | Will this research be helpful in other countries outside Saudi Arabia? |
| Answer: | Yes, if the civil calendar (Ummul Qura) of Saudi Arabia is changed to a predicted crescent visibility (Imkan Al-Ruyat) model then it will help other countries, since some groups in many other countries follow their civil calendar due to the respect for Hajj and Umrah (pilgrims), leading to potential United Eid celebrations, InShaAllah. [Download 1440 AH calendar] |
| Question: | Is it possible to display the Hijri Date on Websites and/or Mobile Phone Apps based on the NACSA criteria? |
| Answer: | We have recently added the NACSA criteria to our database, so any Website/App developers may use the ICOUK Hijri Date API to display the NACSA Hijri Dates on their devices. Others may use this calendar for local moon sightings and report the results to the ICOP website. |