Solar Eclipse No Indication of Hijriah Calendar’s New Month

The sign of the beginning of the month in the Islamic Hijriah calendar is the appearance of the hilal (crescent moon). Meanwhile, a solar eclipse is the sign of the Moon’s entry into its new phase.

KOMPAS/RADITYA HELABUMI

A researcher and engineer from the National Research and Innovation Agency (BRIN) prepares equipment to be used for observing a total solar eclipse at the Earth Station Facility Building, Biak Numfor, Papua, Wednesday (19/4/2023).

A solar eclipse is the conjunction or alignment between the Sun, Moon and Earth that can be observed. Although this conjunction is the sign of the entry into a new phase of the moon, it is not automatically the sign of the arrival of a new month in the Islamic calendar. Of the many lunar calendar systems, the Islamic calendar is the only one that is of an astronomical nature or based on observation.

The ijtimak (conjunction) that signals the beginning the new month of Syawal, the 10th month of the Islamic calendar, according to data from the Meteorology, Climatology and Geophysics Agency (BMKG), this year falls on Thursday, 20 April 2023, coinciding with 29 Ramadhan Hijriah 1444 at 11.12.25 western Indonesia time. This conjunction lasts for around four minutes before the peak of the hybrid solar eclipse on 20 April that takes place south of the waters of Timor Leste at 13.16.45 eastern Indonesia time.

“The sign of the beginning of the month in the Hijriah calendar is the hilal, instead of a solar eclipse,” said calendar researcher and lecturer of the Atmospheric and Planetary Science Study Program, Sumatra Institute of Technology, Moedji Raharto, on Wednesday (19/4/2023). The definition of hilal widely used at present is the first crescent moon observed after the post-conjunction sunset.

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In the case of the end of Ramadhan 1444 H, the sign of the beginning of the month is the appearance of Syawal hilal. A solar eclipse is a topocentric phenomenon on the Earth surface that can happen around the time of a conjunction, both before and after it. Meanwhile, hilal is a geocentric phenomenon, meaning it is measured from a planet or object’s core, each of which has its own size. Consequently, when observed from the Earth’s surface as the Sun is setting, the Moon will have a certain height and elongation.

Although the conjunction of the Sun, Moon and Earth is the sign of the beginning of the new month in the Hijriah calendar, a solar eclipse does not occur every month. This happens, according to acting head of the Center for Technical Seismology, Potential Geophysics and Time Signs of the BMKG, Muzli, at a Science Cultural Bridge seminar of the Total Solar Eclipse Festival in Biak, because the plane of orbit of the Moon around the Earth does not combine with that of the Earth around the Sun.

The Moon’s orbit is tilted by 5 degrees to the plane of orbit of the Earth. As a result, in the view of Thomas Djamaluddin, professor of Astronomical and Astrophysical Research, the National Research and Innovation Agency (BRIN), on a separate occasion, a solar eclipse during a conjunction will only take place if the Moon’s ecliptic latitude is 0-1 degree. “If the Moon’s ecliptic latitude during ijtimak reaches 1-5 degrees, the ijtimak will not be observable or no solar eclipse will occur,” he said.

FAKHRI FADLURROHMAN

Silhouette of an officer observing the new moon at the Al-Musyari'in Mosque, Jalan Basmol Raya, West Jakarta, Wednesday (22/3/2023). The DKI Jakarta Al-Hidayah Basmol Islamic Boarding School Falakiyah Institute team monitors the new moon to determine the first day of Ramadhan 1444 Hijriah.

Beginning of the month

In other lunar calendars, such as the Chinese calendar, the day of ijtimak is determined as the first day in the new month of their calendar. This model of determining the start of the month is called the mathematic model, or one based on hisab or hisab hakiki calculations, which is hisab on the basis of the real condition of sky objects. Apart from being simple, this model also makes sure that the full moon occurs precisely in the middle of the month.

However, the method is not used in determining the start of the month in the Islamic calendar. For the entry into a new month of the Hijriah calendar, after a conjunction, these are several criteria to be adhered to. But so far there is no single criterion yet for the beginning of the Hijriah month to be used by mass organizations or Islamic countries, so differences in the beginning of Ramadan, Idul Fitri and Idul Adha (Day of Sacrifice) are frequently found.

In Indonesia, today at least there are two major criteria applied, which are the criterion of wujudul hilal or hilal materialization as the guide of Muhammadiyah and the new criterion of the Religious Affairs Ministers of Brunei Darussalam, Indonesia, Malaysia and Singapore (MABIMS) used by the Religious Affairs Ministry, Nahdlatul Ulama and a number of other Islamic mass organizations. Other than these two, there are still many criteria applied by small groups of Indonesian Muslims.

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The wujudul hilal criterion is used by the method of hisab hakiki. This calculation is meant to distinguish it from other hisab systems, such as hisab urfi, which is based on the average orbit time of the Moon and Earth around the Sun. An example of hisab urfi is the Javanese calendar that fixes 30 days for odd-number months and 29 days for even-number months.

In the new MABIMS criterion formulated on the basis of hisab, regarding the possibility of seeing the hilal, also known as the imkannur rukyat, it is indicated that hilal can be observed if its height reaches 3 degrees and elongation 6.4 degrees. At present, the elongation used in Indonesia is a geocentric elongation or measurement from the Earth’s core, while in three other MABIMS countries they use topocentric elongation or measurement from the Earth surface.

This article was translated by Aris Prawira.