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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 University, 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 5, 6 or 7 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. Each year always begins from December 28 - January 3. This changes the month number for July, August, September, October, November and December. 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. Here is a Newton year list on the website and these are the years which contain 53 ISO weeks.

Henry argues that his proposal will succeed where others have failed because it keeps the weekly cycle perfectly intact and therefore respects the Fourth Commandment [1]. This calendar also urges people for adoption and attempts to convince people it is the best calendar ever proposed. Henry tells supporters of other calendar proposals to support a switch to the C&T.

However, other calendar proposals that intercalate entire weeks do exist, such as the Symmetry454 calendar. He had advocated transition to the calendar on January 1, 2006 as that is a year in which his calendar and the Gregorian calendar begin the year in sync. But since that date has been missed and so did he miss dropping off December 31, 2006, he recommends simply dropping December 30, 2007 and December 31, 2007 from the calendar and starting on January 1, 2008. Henry says he feels really disappointed^{[citation needed]}.

Robert McClennon's version of the calendar differed from Henry's in that 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 divisible by 400. The main drawback of this rule is that the new year varies 17 days relative to the Gregorian new year.

• Calendar reform

• C&T calendar home page
• Johns Hopkins press release on C&T
• Slashdot discussion of Dick Henry's C&T
• Online Article. "What if We MISS 2006 January 1 Sunday?"