Religious objections The main opponents of the World Calendar in the 20th century were leaders of religions that worship according to a seven-day cycle. For Jews, Christians and Muslims, particular days of worship are ancient and fundamental elements of their faith. Jews observe Saturday as Shabbat, on the basis of the Decalogue's injunction to "remember the sabbath day, to keep it holy" (Exodus 20:8). Most Christians worship on Sunday, the Lord's Day, on which they believe Christ rose from the dead. Muslims perform the jumu'ah prayer in Mosques on Fridays, the day they believe Adam was created. Likewise, Seventh-day Adventists are required to worship every Saturday. Adherents of these religions object that intercalary days are counted outside the usual seven-day week and disrupt the traditional weekly cycle. A week with a Worldsday would be eight days long. Some adherents of these religions insist that they would have to continue observing their holidays every seventh day, causing the worship days to drift by one day each year (two on a leap year), relative to the World Calendar week. The day of rest would then no longer coincide with the weekend. These concerns played a role in the United States government's decision, at the United Nations, in 1955, not to recommend further study. Supporters of the World Calendar do not deny that their system is at odds with the traditions of a significant portion of the world's population, but argue that Worldsdays and Leapyear Days can be treated as "double" holidays by those who wish to maintain the seven-day week sequence. International standards The World Calendar, unlike some other proposals, is not compatible with the international standard ISO 8601, which is based upon, but differs from, the Gregorian calendar. They differ regarding the first weekday of the week (Sunday vs. Monday), and ISO 8601 does not support intercalary dates (e.g. in notation). The World Calendar, however, modifies the Gregorian calendar less than other calendar reform proposals to achieve the sought after improvements of a simpler and perpetual calendar. See also List of calendars World Season Calendar, proposed by Isaac Asimov in 1973, with similarities to the World Calendar International Fixed Calendar, a 13-month calendar reform proposed around the same time as the World Calendar Hanke-Henry Permanent Calendar, a leap-week perennial calendar proposal, which avoids the religious opposition to the World Calendar References External links The World Calendar Association Website (archived September 22,