it in this calendar. Some propose to improve leap rules of existing calendars, such as the Hebrew calendar. The Rectified Hebrew calendar uses a more accurate leap cycle of 4366 months per 353-year cycle, with 130 leap years per cycle, and a progressively shorter molad interval, intended to replace the 19-year leap cycle and the constant molad interval of the traditional fixed arithmetic Hebrew calendar, respectively. Naming Calendar proposals that introduce a thirteenth month or change the Julian-Gregorian system of months often also propose new names for these months. New names have also been proposed for days out of the week cycle (e.g., 365th and leap) and weeks out of the month cycle. Proposals to change the traditional month and weekday names are less frequent. The Gregorian calendar obtains its names mostly from gods of historical religions (e.g., Thursday from Nordic Thor or March from Roman Mars) or leaders of vanished empires (July and August from the first Caesars), or ordinals that got out of synchronization (September through December, originally seventh through tenth, now ninth through twelfth). Examples Comte's Positivist calendar, for example, proposed naming the 13 months in his calendar after figures from religion, literature, philosophy and science. Similarly, the Hermetic Lunar Week Calendar uses 12 or 13 lunar months named after 13 contributors to research on psychoactive plants and chemicals. Specific proposals There have been many specific calendar proposals to replace the Gregorian calendar: The following count one or more days outside the standard seven-day week: International Fixed Calendar Invariable Calendar Positivist calendar World Calendar World Season Calendar The following are leap week calendars: Hanke-Henry Permanent Calendar Pax Calendar Symmetry454 There have also been proposals to revise the way years are numbered: Anno Lucis Holocene calendar Reform of the Islamic calendar: Since the beginning of the 21st century, there is a trend within the Muslim communities of North America and Europe to substitute a lunar calendar based on calculations for the traditional Islamic method of monthly observation of the new moon to declare the beginning of the new month in each country separately. See also Abolition of time zones Determination of the day of the week Decimal calendar Hanke–Henry Permanent Calendar List of calendars Metric time Precursors of the Gregorian reform Johannes de Sacrobosco, De Anni Ratione ("On reckoning the years"), c. 1235 Roger Bacon, Opus Majus ("Greater Work"), c. 1267 References Further reading Segura, Wenceslao (2012). La