A new critique, published as a chapter in the new textbook “Calendars and Years II: Astronomy and Time in the Ancient and Medieval World” (Oxbow Books, 2010), argues that the accepted conversions of dates from Mayan to the modern calendar may be off by as much as 50 or 100 years. That would throw the supposed and overhyped 2012 apocalypse off by decades and cast into doubt the dates of historical Mayan events. (The doomsday worries are based on the fact that the Mayan calendar ends in 2012, much as our year ends on Dec. 31.)