14. Appendix 3 – Use of Optical Aid
The persistent adverse weather conditions of the UK make it difficult to see the youngest crescent moon (Hilal), which could be easily seen by the naked eye in perfect weather conditions in nearby countries (e.g. Morocco).
However, the excellent improvements made in the manufacture of telescope optics and computerised mounts in recent years mean, it is now possible to see the crescent moon by high-powered optical telescopes well beyond the capacity and capability of the average human eyesight.
The role of the telescope is not to create an object that does not exist (but rather to enhance the sighting of an object by making it bigger and brighter) without causing the premature date change (e.g. by CCD imaging) of a visibility-based calendar.
Therefore, it has been recommended to add this guidance note to the ICOUK Moon Sighting Criteria (2017), as stated below.
- The use of optical aid is allowed in the UK provided the moon is possible to be sighted by the average naked eye of correct vision anywhere within the sighting zone (Matale), but not otherwise.
- The sighting zone currently agreed includes the UK to Morocco region, which may change in the future as the number of sighters increases to combat adverse weather conditions in the UK.
- The possibility of the sighting (Imkan Al-Ruyat) by the naked eye is defined as per HMNAO/Yallop Code A (or B above age 24 hrs)*, as informed by UK observation experiences over many years.
*or the equivalent in other published criteria (e.g. Odeh, NACSA, etc).
Note: the purpose of restricting the use of optical aid above is to keep the moon sighting experiences within the reach of the general public (Ruy’yat Ammah) and not just for the selected few (e.g. astronomy experts)!
If you have any comments or questions regarding this criteria, please do not hesitate to email us via our on-line Contact Us form.