The first sighting of the new crescent moon is used as the basis of various calendars to signal the start of the new month. For instance, Islam requires that the sighting of the new crescent moon should be made with the naked eye.
In Islam, moonsighting is an important factor as it determines the new moon (Hilal) as a sign when the fasting month of Ramadhan begins and ends, as well as marking the start of the month of Syawal to celebrate Aidilfitri and the determination of Aidiladha celebration. Such method used is known as Ru'yah. Another method is based on astronomical calculation called as Hisab.
The determination of the new crescent moon varies in several countries. There are some countries that only used the Ru'yah, while the others use Hisab or both of them. Despite Muslims countries have mastered the advanced technology of astronomy by using the Hisab method, some countries apparently still prefer to use Ru'yah by referring to a hadith (Prophet's tradition) narrated by Imam Bukhari that stated, "Do not fast unless you sight the crescent, and do not break your fast till you sight the (following) crescent."
According to moonsighting.com, there are 40 countries have adopted some kind of pre-calculated Islamic calendar. Bangladesh, India, Pakistan, Oman, Morocco, Trinidad, for instances, use actual sighting which is judged by a group of Qadis or the Review Panel. Saudi Arabia, on the other hand practices sometimes determines the birth of the new month by by sighting moon born before sunset in Mekah, and moonset needs to be after sunset in Mekah.
Several countries such as Qatar, Kuwait, United Arab Emirates, Bahrain, Yemen and Turkey follow Saudi Arabia. Egypt determines birth of new crescent and moon sets at least five minutes after sunset. Other countries that use announcements from neighbouring countries are New Zealand that gets it from Australia, and Suriname that gets it from Guyana. Some Caribbean Islands follow the first Muslim country that announces the sighting of the new moon.
There are some countries that use criteria of age, or altitude, or sunset-moonset lag like Algeria and Tunisia. Another country in the northern Africa even sights moon born before Fajr time in the country is Libya.
Meanwhile, three Southeast asian countries Malaysia, Brunei and Indonesia observe and determine the hilal based on the age of the moon, namely its age more than eight hours with altitude of more than two degrees and elongation of more than three degrees. While the only country that has no specific criterion, but its decision varies year by year is Nigeria.
Brunei Darussalam is one of the countries that follows the hadith narrated by Imam Bukhari as mentioned above and has its own moon sighting hills throughout the country. The moonsighting locations in Brunei are Bukit Shahbandar in Jerudong, Bukit Ambok and Padang Tembak Bukit Agok in Tutong, and Bukit Lumut in Belait. The sightings of the new month will be reported to the authority and announced through radio and television by the high court Syariah judge.
According to Rozan Yunos, the writer on the Golden Legacy series published in The Brunei Times, moonsightings in Brunei in the past were conducted at the minaret of Sultan Omar Ali Saifuddien Mosque in Bandar Town as it was considered one of the higher places in the country. Whether the moon was sighted or not, it will be presented to His Majesty the Sultan and Yang Di-Pertuan of Brunei Darussalam before it is announced. The announcement was conducted by using canon volleys, badok (big drums) and if it did not come up people just followed the neighbour country (Sarawak)'s announcement of the first month of Ramadhan.
Brunei has a community of astronomers who called themselves "Persatuan Astronomi Negara Brunei Darussalam" (The Astronomical Society of Brunei Darussalam). They diligently conduct observations and give services on the current development of astronomy, including moonsighting, Kiblat direction, schedules of the Sun and the Moon, schedule of the planets, as well as star charts and planet positions.
The community also released an interesting table which shows the dates of possible first sighting of new moon crescent for Brunei from 2000 to 2099. The Brunei Times