The Criteria

Islamic Calendar Criteria: New Moon (Conjunction)

The basis of the Islamic calendar is the New Moon or the birth of the moon (Gumma/Amavasi). As mentioned in Quran 2:189, observing the various phases of the moon is the best way to determine the end of a month or the beginning of a new one. In its journey across the sky, the moon’s phases wax and wane (Quran 2:189). This movement is determined by Allah with absolute precision (10:5). By observing these phases, we can easily find the exact day a new month begins.

In the final stage of a month, the illuminated part of the moon thins out and eventually appears very slender near the eastern horizon just before dawn. The Holy Quran describes this in 36:39 as “al-Urjun al-Qadim” (like an old, withered date-stalk). Upon reaching this stage, an observer can be certain that the moon will not be visible the following day. This day is the Day of Conjunction (Amavasi), which serves as the final day of the month. This conjunction is itself a phase of the moon. The word ‘Gumma’ in the Prophet’s narration (“Fa in Gumma Alaikum…”) specifically refers to this conjunction/Amavasi.

According to both Sharia and astronomical principles, the global day (Universal Day) on which the conjunction occurs is considered the last day of the month. Regardless of the specific time of conjunction or the difference between sunset and moonset in Makkah or elsewhere, the new month begins from the dawn of the following day.

Global Islamic Calendar and the International Date Line (IDL)

A calendar must always be globally uniform because a “day” is a global phenomenon. Consequently, the date must also be global. Therefore, there must be a specific place on Earth where a day begins. For example, Friday begins in the New Zealand region and spreads across the world as it moves westward. This is the system the world follows. Only by following this same concept in the Islamic calendar can the day of Friday correspond to a single date across all countries.

Some argue that the current International Date Line (IDL) was fixed by the British and has no basis in Islam. This is entirely incorrect. Just as America existed long before Columbus “discovered” it, the day began from that specific region long before humans gave it a name. The Islamic calendar is a system combining solar days and lunar phase dates, established by Allah since the beginning of the universe (9:36).

The Conjunction and the Start of the New Month

When it is said that the new month starts the day after the conjunction, certain doubts may arise. For instance, would those in the eastern region near the Date Line have to enter the new month before the conjunction actually occurs globally? Similarly, would those in the western region have to wait an extra day even after observing the conjunction?

We must note an important point here: the day and date of the conjunction are recorded much like a person’s birth. For example, the Prophet (ﷺ) was born in Makkah on a Monday. At that exact moment, it might have been a different day in another part of the world (like America). However, because of the place of birth, that day is recorded as Monday globally.

Accordingly, the day of the moon’s birth—the moment the moon overtakes the sun—is recorded based on the day at the Geographical Position (GP) where it occurs. If it occurs on a Friday in New Zealand, the day of conjunction is Friday. (Note that it would still be Thursday in Canada at that time). It is not the specific time of conjunction that matters, but the day at the place of occurrence. In this case, the new month begins for everyone on Saturday.

Conversely, if the conjunction occurs on a Friday in the Canada region (west of the IDL), it would already be Saturday for people in the eastern part (New Zealand).

In short: Everyone enters the new month on the day immediately following the “Day of Conjunction,” determined by the geographical location where the conjunction occurs.

While it is true that some islands and countries have altered the Date Line for commercial or political reasons, such individual decisions do not affect the fundamental principle of the International Date Line.