2. Introduction

In the Islamic calendar, traditionally, the first visibility of the new Moon to an unaided human eye marks the beginning of the month. In particular, sighting is considered essential regarding the start of Ramadan and the two Eids in order to comply with the rulings of the Shariah, which is based on our Prophet’s practice (PBUH) in the period when no other scientific means were available. However, the unreliability of the dependence on physical visibility has led not only to wide variations in the three important dates within the same country, but also to a great disunity among the Muslim communities throughout the world. It is, therefore, necessary to examine these visibility criteria scientifically before drawing any conclusions as to its usefulness and its replacement with any other method. It is also necessary to examine what the Qur’an has to say on this matter and whether the scientific approach has any contradictions with what is stated in the Qur’an. To understand the visibility criteria it is necessary to look at both the astronomical and physical aspects involved in a sighting with the naked eye as well as the methods used for terrestrial and celestial measurements.