arbitrary imposition, the question can arise as to which Saturday on either side of the Date Line (or, more fundamentally, on either side of 180 degrees longitude) is the "real" Saturday. This issue (which also arises in Judaism) is a particular problem for Seventh Day Adventists, Seventh Day Baptists, and similar churches located in countries near the Date Line. In Tonga, Seventh Day Adventists (who usually observe Saturday, the seventh-day Sabbath) observe Sunday due to their understanding of the International Date Line, as Tonga lies east of the 180° meridian. Sunday as observed in Tonga (West of the Date Line, as with Kiribati, Samoa, and parts of Fiji and Tuvalu) is considered by the Seventh-day Adventist Church to be the same day as Saturday observed East of the Date line. Most Seventh Day Adventists in Samoa planned to observe Sabbath on Sunday after Samoa's crossing the date line in December 2011, but SDA groups in Samatau village and other places (approx. 300 members) decided to accept the IDL adjustment and observe the Sabbath on Saturday. Debate continues within the Seventh-day Adventist community in the Pacific as to which day is really the seventh-day Sabbath. The Samoan Independent Seventh-day Adventist Church, which is not affiliated to the worldwide Seventh-day Adventist Church, has decided to continue worshiping on Saturday, after a six-day week at the end of 2011. Islam Similarly, the Islamic calendar and Muslim communities recognize the convention of the IDL. In particular, the day for holding the Jumu'ah prayer appears to be local Friday everywhere in the world. The IDL is not a factor in the start and end of Islamic lunar months. These depend solely on sighting the new crescent moon. As an example, the fasts of the month of Ramadan begin the morning after the crescent is sighted. That this day may vary in different parts of the world is well known in Islam. (See .) Judaism The concept of an international date line in Jewish law is first mentioned by 12th-century decisors. But it was not until the introduction of improved transportation and communications systems in the 20th century that the question of an international date line truly became a question of practical Jewish law. As a practical matter, the conventional International Date Line—or another line in the Pacific Ocean close to it—serves as a de facto date line for purposes of Jewish law, at least in