Common year starting on Sunday

A common year starting on Sunday is any non-leap year (i.e., a year with 365 days) that begins on a Sunday, January 1 (dominical letter A). Examples: Gregorian years 1978, 1989, 1995, 2006, 2017, 2023, 2034, and 2045 or Julian year 1917. See the tables at the end of the article.

Hence, a common year can be represented thus:

Notes

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

Sunday

Sunday (ⁱ/ˈsʌndeɪ/ or /ˈsʌndi/) is the day of the week following Saturday but before Monday. For most Christians, Sunday is observed as a day of worship and rest, holding it as the Lord's Day and the day of Christ's resurrection. Sunday is a day of rest in most Western countries, part of 'the weekend'. In some Muslim countries and Israel, Sunday is the first work day of the week. According to the Hebrew calendars and traditional Christian calendars, Sunday is the first day of the week, and according to the International Organization for Standardization ISO 8601 Sunday is the seventh and last day of the week. No century in the Gregorian calendar starts on a Sunday, whether its first year is considered to be '00 or '01. The Jewish New Year never falls on a Sunday. (The rules of the Hebrew calendar are designed such that the first day of Rosh Hashanah will never occur on the first, fourth, or sixth day of the Jewish week; i.e., Sunday, Wednesday, or Friday).

Etymology

Sunday, being the day of the Sun, as the name of the first day of the week, is derived from Hellenistic astrology, where the seven planets, known in English as Saturn, Jupiter, Mars, the Sun, Venus, Mercury and the Moon, each had an hour of the day assigned to them, and the planet which was regent during the first hour of any day of the week gave its name to that day. During the 1st and 2nd century, the week of seven days was introduced into Rome from Egypt, and the Roman names of the planets were given to each successive day.

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.