The moon is the earth’s dark satellite, visible only by reflecting the light of the sun. The visible area of the moon changes daily according to the angle formed by line between the sun, the earth and the moon, which results in the cycle of lunar phases.

The Hijri calendar depends on a natural phenomenon that determines the beginning of lunar months. It’s in compliance with the Qur’an (Surat Al-Baqarah 2:189), “They ask thee about the new moons. Say, ‘they are but signs to mark fixed points of time for people [to manage their affairs], and [to identify the time of] hajj.’”

Of particular concern to Muslims are the fasting month of Ramadan and the month of hajj. A lunar month’s start is identified by sighting the waxing crescent after sunset on the 29th or 30th of the foregoing month.

A lunation is the average time from one new moon to the next. The average length of a lunation is 29 days, 12 hours, 44 minutes, and 2.8 seconds. In a lunar calendar, each month corresponds to a lunation.

In non-astronomical contexts, new moon refers to the first visible crescent of the Moon, after conjunction with the Sun. This takes place over the western horizon in a brief period between sunset and moonset. Therefore the precise time and even the date of the appearance of the new moon depends on the geographical location.

On the other hand, the astronomical new moon, sometimes known as the ‘Dark Moon’ to avoid confusion, occurs at the moment of conjunction in ecliptic longitude with the Sun, when the Moon is invisible from the Earth. This moment is unique and doesn’t depend on location

Everywhere in the Muslim world, sighting the waxing crescent is important. In addition to setting the calendar, it also determines the dates of important religious occasions. But sighting the crescent has always been a controversial issue in the Islamic world.

In some places, observers can spot it easily whereas in others they may not. There have been incidents of inaccurate sighting reports. Such incongruities call for Muslim astronomers to put an end to differences in this regard.

Celestial Mechanical View

The moon, like the planets, has a slightly elliptical orbit. To determine its apparent position, particularly as a waxing crescent, an observer makes several measurements. These measurements include its distance from the sun, its position in relation to a specific observer on earth. And moreover, the exact time of its rising and setting.

Detailed tabular calculations of the moon’s motion were produced in the 19th century by the astronomer Ernest William Brown. These tables were improved by 20^th century astronomers who developed equations to determine the exact position of the moon.

Muslim astronomers have developed computer software to identify the position of the earth in its orbital movement round the sun.

The point is to determine accurately the time of sunset. And consequently, the exact position of the crescent using the equations derived from Brown’s lunar tables.

Medieval Muslim astronomers like Al-Battani, Al-Bayrouni, and Nassir al-Din Al-Tousi have accruatlyyy calculated the lunar months.

In the 19^th century, an Egyptian army general, Mohamed Mokhtar Pasha, produced a valuable work on tabular correlations of the Muslim calendar, the Gregorian calendar and the ancient luni-solar system of time reckoning.

The tables cover the Muslim calendar from years 1 through 1500 and the matching dates under the other two systems.

What Shari’ah Says

According to Shari’ah, to establish the beginning of the new lunar month, the crescent must be sighted by the naked eye under specific conditions. The sighting may, however, be influenced by a number of factors including:

• the life-length of the crescent, and the angle it forms with the sun;
• the height of the crescent relative to the horizon line at the time of sunset;
• the distance between the earth and the moon;
• weather conditions and the degree of visibility.

The first two factors are essential. The third is only partially important. That’s because the distance between the earth and the moon changes by approximately ± 4% only. This small rate has a negligible effect on visibility.

The fourth factor depends on variable local conditions at the time of sighting the crescent.

In 1978, the Islamic jurisprudence committee of the Islamic Conference (OIC) set the following conditions for the crescent sighting:

• The angle of the crescent’s position above the horizon at sunset must be at least 5 arc degrees;
• The angle formed by the moon and the sun must be at least 8 arc degrees. 

When these two most essential conditions are there, the following day shall be the first day of the new month.

The motion of the moon can now be calculated with great precision, but the beginning of every new lunar month remains a problem.

Surveys will have to be conducted in various places in the Islamic world for several years for sufficient statistical analysis. If this is done, differences between Muslim countries in marking religious occasions may be finally overcome.

Prophetic Advice

Whenever faced with two or more options, Prophet Muhammad (SAW) always chose the easier. The Qur’an (Surat At-Tawbah 9:128) describes him as being extremely commiserating and willing to spare the Muslims suffering and hardship.

Surat Al-Baqarah 2:185 also tells us that God intends every facility for the faithful. He doesn’t will putting them to unaffordable tasks in life.

Shari’ah was therefore satisfied with what was within the means of the Prophet’s companions. This, however, doesn’t mean that new scientific methods are to be excluded. This seemingly contradiction of views calls for a closer look.

Early Muslim scholars were almost unanimous in rejecting astronomical methods during their time. To them, there was no clear line of demarcation between astronomy and astrology.

However, modern astronomy is different. It draws on spherical geometry and celestial mechanics. These two modern branches of science enabled man to land on the moon over a quarter of a century ago.

Nowadays

According to Dr. Mostafa Al-Zarqa, a leading Muslim scholar, the debate on the legitimacy of astronomical calculation is the greatest oddity in modern jurisprudence, remaining hot at a time when man has navigated the vast expanses of the universe, and landed on the moon.

At the present time, landing on the moon is no longer a great feat. All relevant Hadith suggest that sighting the moon with the naked eye was the only method available back then because the majority of the Muslim population was illiterate.

This by no means excluded verifiable scientific methods that are capable of yielding extremely accurate results. The naked-eye method is perfectly acceptable when conditions of clear visibility are available.

Otherwise, there is no reason behind not relying on scientific calculations. It’s a shame that there is sometimes a three-day discrepancy between Muslim countries in deciding Ramadan dates.

Futuristic Approach

The position of early Muslim jurisprudents to reject guessing and intuition as sources of reliable knowledge on this particular issue is understandable. Astronomy was still controversial at that early stage of Islam, Al-Zarqa explains.

Decades ago, the Fatwa House in Egypt decided that the naked-eye sighting is the standard method of observing the lunar months.

According to the Fatwa House, we can use astronomical measurements only as a supportive tool. Not as an alternative. But, we must reject sighting reports that contradict accurate measurements. That’s because Islam exhorts its followers to resort to the proper channels of learning and knowledge.

Meanwhile, with the approach of every new Ramadan, the same controversy around deciding its dates renews. Muslim countries observe Ramadan and other important religious occasions on different days because of a lack of standardization.

This article is from Science’s archive and we’ve originally published it on an earlier date.