7. Moon Sighting Calculations
7.1 The Holy Quran clearly states: “The sun and the moon follow course [exactly] computed” (Quran 55:5) /http://tanzil.net/#55:5
Observation experience over many years has also proven the accuracy of the position of the sun and the moon, especially during the times of solar eclipses, which visually shows the accuracy of New Moon Conjunction (NMC).
However, the calculations of crescent moon visibility are very complex and it was not possible until 1990’s when high powered personal computers became accessible to researchers who were able to produce more accurate models that matched the actual sightings and started a revolution in predicting crescent moon visibility.
The ICOP group started collecting actual observation data since 1998 using Dr Bernard Yallop of HM Nautical Almanac Office (UK) visibility model and by 2006, an improved model was published by Engineer Mohammad Odeh, which shows both the waxing and waning phases of the moon to a high degree of accuracy (see below).
From the above visibility maps for waning and waxing crescent moon, as verified with actual observations, the duration of the New Moon Phase (Mahaq) is about 60 hours (2.5 days) long and in extremely rare cases it may be about 36 hours (1.5 days) long if both the waning and waxing crescent can be seen 18 hrs before and after NMC.
Regarding the phases of the moon, Allah says:
"And (as for) the moon, We have measured for it mansions/phases (to traverse) till it returns like the old dried curved date stalk (Urjoonil Qadim)." [Quran 36:39] / http://tanzil.net/#36:39
In the Tafsir Jalalyan of the above verse it is stated there are visible and invisible phases of the moon (Mahaq), i.e. when it cannot be seen (for 1 or 2 days in each month). Therefore, the predicted crescent visibility maps, simply confirm the visible and invisible phases of the moon, which is consistent with the Quran and Ahadith.
7.2 There are three types of visibility maps that are widely used over past 10 years and while the ones by Eng Khalid Shaukat (USA) and Eng Mohammad Odeh (UAE) are very similar, the one by Dr Barnard Yallop (UK) is slightly different.
The visibility maps by Dr Barnard Yallop of HM Nautical Almanac Office (HMNAO) was first published in 1997 based on naked eye and small telescope sightings. However, due to advancement in technology with improved optics and computerised telescopes, more recent world-record sightings have been incorporated by Shaukat and Odeh criteria in 2005 - 2006.
Dr Barnard Yallop has retired many years ago and the present Head of HMNAO (Dr Steve Bell) was requested by ICOUK (in 2012 – 2015) to make a number of improvements to their old visibility maps, such as to include more recent world-record by Jim Stamm (USA) to make the curves similar to Shaukat and Odeh criteria (see Appendix).
While they accepted the other suggestions and revised their maps accordingly (astro.ukho.gov.uk/moonwatch), they did not consider one or two world record sighting records were sufficient to change their maps. The ICOUK website prefers to use HMNAO maps (Yallop/A+B), since they are sufficient for the UK adverse weather conditions.
7.3 Using the crescent visibility maps for a given location or region, it is now possible to produce a predicted Hijri Calendar for civil purposes (e.g. for Ramadan/Eid holidays), which will also match actual observations, since cloudiness is a local phenomenon and the whole country or the region is not cloudy at the same time. The tables below show the predicted Hijri Calendar based on the “Regional Moon Sighting Criteria for the UK” as examples.