Lunar months, as implied by their name, are determined by the phases of the moon. Since Ramadan fasting takes place during the month of Ramadan and the month itself shifts each year according to the lunar calendar, determining the start of Ramadan is essential for beginning the fast. The Prophet Muhammad (peace be upon him) instructed, “Begin fasting upon sighting the crescent (of Ramadan) and break the fast (celebrate Eid) upon sighting the crescent (of Shawwal). If it is cloudy, complete thirty days of the current month” (Muslim, Sawm, 19-20 [1081]; also see Bukhari, Sawm, 5, 11 [1900, 1909]).
At first glance, this hadith suggests that fasting should only start and Eid should only be celebrated when the crescent is seen with the naked eye. However, considering other hadiths on the topic reveals that these instructions were intended to teach the most appropriate approach for that time. In another narration, the Prophet (peace be upon him) stated, “We are an unlettered community; we do not write or calculate. The month is either 29 or 30 days” (Bukhari, Sawm, 13 [1913]; Muslim, Sawm, 15 [1080]). This indicates that using calculations was not forbidden but simply uncommon, pointing to the possibility of employing calculation methods to determine the lunar months.
The moon continues its natural phases whether seen or not. The Quran mentions that both the sun and the moon move according to a fixed reckoning (Ar-Rahman, 55:5), and that these celestial bodies serve as measurements for time, aiding humanity in tracking months and years (Yunus, 10:5). The Quran also refers to the moon’s gradual appearance in different phases, which assists people in marking time and setting dates (Al-Baqarah, 2:189).
Thus, the Prophet’s emphasis on visually sighting the crescent was not due to its being the only legitimate method, but rather because it was the most reliable option given the limitations of that era. The purpose of crescent sighting is simply to confirm the arrival of Ramadan. Therefore, it is permissible to use any method that reliably achieves this goal, including calculation-based approaches.
With today’s technological advancements, we can track lunar movements with remarkable accuracy. Precise astronomical calculations can even create prayer timetables for years in advance. Therefore, determining the start of lunar months through calculations is acceptable in Islam, as it aligns with the purpose of marking time in accordance with the lunar calendar.