The Common-Civil-Calendar-and-Time calendar (C&T) is a proposal for calendar reform. It is one of many examples of leap-week calendars, calendars which maintain synchronization with the solar year by intercalating entire weeks rather than single days.

In 2004, Dick Henry, a professor of astronomy at Johns Hopkins, proposed the adoption of a calendar which he credits to Robert McClennon. It is very similar to the Gregorian calendar but is identical from year to year in most years. It is kept in sync with the Earth's orbit by adding a whole intercalary week-long period, named "Newton," at irregular intervals of five or six years. January, February, April, May, July, August, October, and November have thirty days, March, June, September, and December have thirty-one. "Newton" week, in years that contain it, falls between June and July. The list of years that contain "Newton" week must be calculated by computer or obtained from a table or almanac, as it follows no simple rule. Henry argues that his proposal will succeed where others have failed because it is the only one that keeps the weekly cycle perfectly intact and therefore respects the Fourth Commandment. However, other calendar proposals that intercalate entire weeks do exist, such as the Symmetry454 calendar. He advocates transition to the calendar on January 1st, 2006 as that is a year in which his calendar and the Gregorian calendar begin the year in sync.

Robert McClennon's version of the calendar has the leap week at the end of the year, thereby ensuring that each date of the year is the same day number of the year. Also it has a simple rule for determining which years have a leap week. This rule resembles the Gregorian Leap Year rule. Years whose numbers are divisible by 5 have a leap week, but years whose numbers are divisible by 40 do not have a leap week unless also divisble by 400. The main drawback of this rule is that the new year varies 17 days relative to the Gregorian new year.

External links

• C&T calendar home page
• Leap-week Calendars
• Johns Hopkins press release on C&T
• Slashdot discussion of Dick Henry's C&T
• Find other information/articles on the Common-Civil-Calendar-and-Time proposal