I want to shed some light on the recent conversations about moon sighting, the lunar calendar and the use of scientific information to determine the start of Islamic months.

In Pakistan, it has been a practice to sight the moon to commence a lunar month. Recently, it has been proposed that since this is the age of science, we should benefit from research data and stop relying on moon sighting.

Certainly, we should rely on scientific observations and computations, but does that necessarily mean we should do away with moon sighting entirely? Traditionally, sighting the moon has been a requirement and even today, it does serve a purpose.

The science

The moon follows a set course and passes through different phases. The lunar conjunction, or the new moon, takes place when the moon, after its course, arrives exactly in front of the sun — and the sun, moon and earth are in a straight line.

At the sunset that occurs after conjunction, the moon remains on the horizon for some time (possibly for even a minute). The size and the duration of the existence of the moon depends on the age (time since conjunction) of the moon. The smaller the duration between sunset and conjunction, the smaller the size of the moon and smaller the duration of its existence on the horizon.

The visibility of the moon after sunset primarily depends on two factors: the elongation and altitude of the moon.

Elongation, or the arc of light, refers to the angular separation of the moon from the sun as observed from earth. Scientists state that, for the new moon to be seen by the naked eye, the elongation should exceed 10 degrees and the altitude of the moon above the horizon should exceed 5° at a time when the depression of the Sun is 3°. If these requirements are met, it will ensure that the crescent is not too thin and that it is visible.

Due to technological progress, astronomical calculations can not only tell us about the visibility of the moon on a particular date, but also provide the following details:

• Birth, age and size of the moon
• Sunset and moonset times
• Duration of the moon on the horizon after sunset
• Elongation
• Altitude of the moon
• Moon visibility maps

Take, for example, the moon visibility maps below for this month of Shawwal. They represent the visibility of the moon for every point (latitude and longitude) on the globe at the time of the local sunset.

It is evident that the moon could not have be sighted (almost) anywhere yesterday, June 3. The moon, however, will be sighted (almost) everywhere on the globe today, June 4.

It is unfortunate that Khyber Pakhtunkhwa announced Eid yesterday without any scientific basis. The only places where it was possible to sight the moon on June 3 were the American west coast, Central and parts of South America — and that even by telescope or other optical aid.

Cautious use of data

We can have approximate predictions whether the crescent can be seen with a telescope, binoculars or the naked eye. But these are predictions and since there are many factors contributing to the visibility of the moon, there is no exact answer as to how the new moon could be sighted.

At most, we can devise a very accurate (estimated) lunar calendar based on scientific observations and calculations, but these will be estimates. The orbits of the earth and the moon slightly change over time and the elongation and altitude requirements also vary, which means predictions of future dates may not be exact.

For example, if we look at the Umm al-Qura calendar followed in Saudi Arabia, which doesn't rely on seeing the moon to mark the start of a month, we will notice that the sighting of the crescent can occur before or after the predicted dates. The analysis for certain months, including Ramazan and Shawwal, for the last 19 years shows that the actual dates of the months were either before or after the predicted dates 21 percent of the time.

Rephrasing the question

Instead of doing away with moon sighting, we should ask if the practice can be coupled with science.

The scientific criteria applied to the sighting of the crescent should be used as a guide so as to eliminate the confusion as to when the crescent is most likely to be seen at a particular geographical location. We should use data for assessing the possibility of moon sighting in a space-time window and for determining the accuracy of moon sighting reports.

If that is done, we won't need to replace the conventional practice altogether and the Ruet-i-Hilal Committee won't have to be abolished either.

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