BRIN Researchers Respond to the Viral Issue of Idul Fitri 2031 Coinciding with Christmas, Here Are the Results

Dream - There is a circulating narrative on social media that claims Idul Fitri in 2031 will coincide with the celebration of Christmas. But is this information true, supported by the narrative of this calendar calculation?

As information, the Hijri calendar uses the kamariah or lunar system which refers to the moon's orbit around the earth. Meanwhile, the Gregorian calendar is made by referring to the period of the earth orbiting the sun.

The difference in the calculation method of the day results in a difference of about 11 days each year. This is what makes Idul Fitri fall on different dates every year.

It is even rumored that Idul Fitri can occur twice a year. The National Research and Innovation Agency (BRIN) revealed that this phenomenon occurs every 32-33 years.

Unlike the celebration of Christmas which uses the reference of the Gregorian calendar, Christians celebrate it every year on December 25th.

Then, there is a narrative that Idul Fitri will coincide with Christmas in 2031. How is the explanation?

Andi Pangerang from the BRIN Space Research Center explained that the moon phase used to mark the change of the month in the Hijri calendar is the youngest initial crescent phase or also called hilal.

This can be seen after sunset if the weather is clear, free from light pollution, and not covered by clouds.

However, according to Andi, there is one more requirement to observe the hilal, which is to see the new moon phase or conjunction.

The new moon phase is the condition when the moon's surface facing the earth is not exposed to sunlight.

"This is because during the new moon, the sun, moon, and earth are located in a straight line when observed from the perpendicular plane of the ecliptic. This condition implies that the moon has the closest angular distance from the sun. Meanwhile, if the new moon is seen above the horizon before the new moon, it is still categorized as the oldest final crescent moon or called muhaq," said Andi, as quoted from the official website BRIN.

Furthermore, Andi stated that the new moon phase used as the initial reference of Syawal is also called the initial Syawal conjunction in 2031 on January 23, 2031 at 11:30 AM WIB/ 12:30 PM WITA/ 1:30 PM WIT.

Andi explained that the toposentric height of the hilal for observation on January 23, 2031 evening in Indonesia varies. It ranges from -0.58 degrees (Merauke) to +2.02 degrees (Sabang).

Meanwhile, the geosentric elongation angle of the hilal-sun varies between 5.10 degrees (Merauke) to 6.14 degrees (Sabang).

With the criteria of hilal visibility currently used in Indonesia (toposentric height > 3 degrees and geosentric elongation < 6.4 degrees), the hilal is difficult to observe, so the 1st Syawal 1452 H falls on January 25, 2031.

Meanwhile, the closest moon phase on December 25 falls on December 14 at 4:05 PM WIB/ 5:05 PM WITA/ 6:05 PM WIT, which is the initial Ramadan conjunction of 1453 H.

The toposentric height of the hilal for observation on the evening of December 14, 2031 in Indonesia varies from -1.58 degrees (Merauke) to +0.37 degrees (Sabang).

Meanwhile, the geosentric elongation angle of the hilal-sun varies between 2.86 degrees (Merauke) to 3.27 degrees (Sabang).

With the criteria of hilal visibility currently used in Indonesia, Andu said that the hilal is difficult to observe, so the 1st Ramadan 1453 H falls on December 16, 2031. Therefore, December 25, 2031 falls on the 10th Ramadan 1453 H.

Meanwhile, the 1st Syawal 1453 H is estimated to fall on January 14, 2032, so Idul Fitri does not coincide with Christmas in 2031.

When Does Idul Fitri Coincide with Christmas?

Andi mentioned that throughout Indonesia's independence, there have been two times when Idul Fitri falls almost close to Christmas. The first time was in 1968 when Idul Fitri 1388 H fell on December 21, 1968. The second time was in 2000 with Idul Fitri 1421 H falling on December 27, 2000.

A similar event will occur again in 2033 and 2065. At that time, Idul Fitri 1455 H will occur on December 23, 2033, and Idul Fitri 1488 H will occur on December 29, 2065.

"If you notice, when Idul Fitri coincides with Christmas, then Idul Fitri will occur around the end of the Gregorian year, so it can be confirmed that Idul Fitri occurs twice in the same Gregorian year," he said.

The first Idul Fitri has already occurred at the beginning of the Gregorian year and some coincide with the new year, such as in 1968, Idul Fitri 1387 H fell on January 2, 1969. Meanwhile, in 2033, Idul Fitri 1454 H will fall on January 3, 2033.