Common year starting on Thursday

This is the calendar for any common year starting on Thursday, January 1 (dominical letter D). Examples: Gregorian years 1981, 1987, 1998, 2009, 2015, 2026, 2037, and 2043 or Julian year 1915 (see bottom tables).

This is the only common year with three occurrences of Friday the 13th (leap years starting on Sundays share this characteristic); February, March and November.

A common year is a year with 365 days, i.e. not a leap year.

This kind of year has 53 weeks in the ISO 8601 week - day format.

References

Common year

A Common year is a calendar year with exactly 365 days, in contrast to the longer leap year. More generally, a common year is one without intercalation. The Gregorian calendar (like the earlier Julian calendar) employs both common years and leap years to adjust for differing astronomical measurements of the year: sidereal and tropical.

The common year of 365 days has exactly 52 weeks and one day, hence a common year always begins and ends on the same day of the week. (For example: both January 1 and December 31 fell on a Friday in 2010). In a common year, February has exactly four weeks, so that month and March always start consecutively on the same day of the week.

In the Gregorian calendar, 303 of every 400 years are common years. By comparison, in the Julian calendar, 300 out of every 400 years are common years.

In the Lunisolar calendar and the Lunar calendar, a common year consists of 354 days.

Calendars

Gregorian calendar

The Gregorian calendar, also called the Western calendar and the Christian calendar, is internationally the most widely used civil calendar. It is named for Pope Gregory XIII, who introduced it in 1582.

The calendar was a refinement to the Julian calendar amounting to a 0.002% correction in the length of the year. The motivation for the reform was to bring the date for the celebration of Easter to the time of the year in which it was celebrated when it was introduced by the early Church. Because the celebration of Easter was tied to the spring equinox, the Roman Catholic Church considered the steady drift in the date of Easter caused by the year being slightly too long to be undesirable. The reform was adopted initially by the Catholic countries of Europe. Protestants and Eastern Orthodox countries continued to use the traditional Julian calendar and adopted the Gregorian reform after a time, for the sake of convenience in international trade. The last European country to adopt the reform was Greece, in 1923.

Julian calendar

The Julian calendar, introduced by Julius Caesar in 46 BC (708 AUC), was a reform of the Roman calendar. It took effect in 45 BC (709 AUC), shortly after the Roman conquest of Egypt. It was the predominant calendar in the Roman world, most of Europe, and in European settlements in the Americas and elsewhere, until it was refined and gradually replaced by the Gregorian calendar, promulgated in 1582 by Pope Gregory XIII. The Julian calendar gains against the mean tropical year at the rate of one day in 128 years. For the Gregorian the figure is one day in 3,226 years. The difference in the average length of the year between Julian (365.25 days) and Gregorian (365.2425 days) is 0.002%.

The Julian calendar has a regular year of 365 days divided into 12 months, as listed in Table of months. A leap day is added to February every four years. The Julian year is, therefore, on average 365.25 days long. It was intended to approximate the tropical (solar) year. Although Greek astronomers had known, at least since Hipparchus, a century before the Julian reform, that the tropical year was a few minutes shorter than 365.25 days, the calendar did not compensate for this difference. As a result, the year gained about three days every four centuries compared to observed equinox times and the seasons. This discrepancy was corrected by the Gregorian reform of 1582. The Gregorian calendar has the same months and month lengths as the Julian calendar, but, in the Gregorian calendar, years evenly divisible by 100 are not leap years, except that years evenly divisible by 400 remain leap years. Consequently, the Julian calendar is currently (since the beginning of March 1900 and until the end of February 2100) 13 days behind the Gregorian calendar; for instance, 1 January in the Julian calendar is 14 January in the Gregorian.