Lunisolar calendar

A lunisolar calendar is a calendar in many cultures whose date indicates both the moon phase and the time of the solar year. If the solar year is defined as a tropical year, then a lunisolar calendar will give an indication of the season; if it is taken as a sidereal year, then the calendar will predict the constellation near which the full moon may occur. Usually there is an additional requirement that the year have a whole number of months. In this case ordinary years consist of twelve months but every second or third year is an embolismic year, which adds a thirteenth intercalary, embolismic, or leap month.

Examples

The Hebrew, Buddhist, Hindu, Kurdish, Bengali, and Tibetan calendars, as well as the traditional Chinese, Japanese, Vietnamese, Mongolian and Korean calendars, plus the ancient Hellenic, Coligny, and Babylonian calendars are all lunisolar. Also, some of the ancient pre-Islamic calendars in South Arabia followed a lunisolar system. The Chinese, Coligny and Hebrew lunisolar calendars track more or less the tropical year whereas the Buddhist and Hindu lunisolar calendars track the sidereal year. Therefore, the first three give an idea of the seasons whereas the last two give an idea of the position among the constellations of the full moon. The Tibetan calendar was influenced by both the Chinese and Hindu calendars. The Germanic peoples also used a lunisolar calendar before their conversion to Christianity.

Calendar

A calendar is a system of organizing days for social, religious, commercial or administrative purposes. This is done by giving names to periods of time, typically days, weeks, months, and years. A date is the designation of a single, specific day within such a system. A calendar is also a physical record (often paper) of such a system. A calendar can also mean a list of planned events, such as a court calendar or a partly or fully chronological list of documents, such as a calendar of wills.

Periods in a calendar (such as years and months) are usually, though not necessarily, synchronized with the cycle of the sun or the moon. The most common type of pre-modern calendar was the lunisolar calendar, a lunar calendar that occasionally adds one intercalary month to remain synchronised with the solar year over the long term.

The calendar in most widespread use today is the Gregorian calendar, introduced in the 16th century as a modification of the Julian calendar, which was itself a modification of the ancient Roman calendar. The term calendar itself is taken from calendae, the term for the first day of the month in the Roman calendar, related to the verb calare "to call out", referring to the "calling" of the new moon when it was first seen. Latin calendarium meant "account book, register" (as accounts were settled and debts were collected on the calends of each month). The Latin term was adopted in Old French as calendier and from there in Middle English as calender by the 13th century (the spelling calendar is early modern).

New moon

In astronomy, new moon is the first phase of the Moon, when it orbits as seen from the Earth, the moment when the Moon and the Sun have the same ecliptical longitude. The Moon is not visible at this time except when it is seen in silhouette during a solar eclipse when it is illuminated by earthshine. See the article on phases of the Moon for further details.

A lunation or synodic month is the mean (average) time from one new moon to the next. In the J2000.0 epoch, the average length of a lunation is 29.530588 days (or 29 days, 12 hours, 44 minutes, and 3 seconds). However, the length of any one synodic month can vary from 29.26 to 29.80 days due to the perturbing effects of the Sun's gravity on the Moon's eccentric orbit. In a lunar calendar, each month corresponds to a lunation. Each lunar cycle can be assigned a unique Lunation Number to identify it.

Determining new moons: an approximate formula

The length of a lunation is about 29.53 days. Its precise duration is linked to many phenomena in nature, such as the variation between spring and neap tides (the extreme highest and lowest tides, respectively). An approximate formula to compute the mean moments of new moon (conjunction between Sun and Moon) for successive months is:

Sabbath

Sabbath (/ˈsæbəθ/) is a day set aside for rest and worship. According to Exodus 20:8 the Sabbath is commanded by God to be kept as a holy day of rest, as God rested from creation. It is observed differently among the Abrahamic religions and informs a similar occasion in several other practices. Although many viewpoints and definitions have arisen over the millennia, most originate in the same textual tradition of: "Remember the sabbath day, to keep it holy".

In Judaism, Sabbath is the seventh day of the Hebrew calendar week, which in English is known as Saturday. The term has been used to describe a similar weekly observance in any of several other traditions; the first crescent or new moon; any of seven annual festivals in Judaism and some Christian traditions; any of eight annual pagan festivals (usually "sabbat"); an annual secular holiday; and a year of rest in religious or secular usage, the sabbath year, originally every seventh year.

Biblical Sabbath

Sabbath (as the verb Shavath) is first mentioned in the Genesis creation narrative, where the seventh day is set aside as a day of rest and made holy by God (Genesis 2:2–3). Observation and remembrance of Sabbath is one of the Ten Commandments (the fourth in the original Jewish, the Eastern Orthodox, and most Protestant traditions, the third in Roman Catholic and Lutheran traditions). Most people who observe the Sabbath regard it as having been instituted as a perpetual covenant for the Israelites (Exodus 31:13–17), as a sign respecting two events: the day during which God rested after having completed Creation in six days (Exodus 20:8–11), and the Israelites' deliverance from Egypt (Deuteronomy 5:12–15). Originally, Sabbath-breakers were officially to be cut off from the assembly or potentially killed (Exodus 31:15). Observance in the Hebrew Bible was universally from sixth-day sundown to seventh-day sundown (Nehemiah 13:19, cf. Leviticus 23:32) on a seven-day week.

Lunar calendar

A lunar calendar is a calendar that is based on cycles of the lunar phases. This can be contrasted with the Gregorian calendar, which is a solar calendar based on the revolution of the Earth around the sun. Because there are slightly more than twelve lunations (synodic months) in a solar year, the period of 12 lunar months (354.37 days) is sometimes referred to as a lunar year.

A common purely lunar calendar is the Islamic (or Hijri Qamari) calendar. A feature of the Islamic calendar is that a year is always 12 months, so the months are not linked with the seasons and drift each solar year by 11 to 12 days. It comes back to the position it had in relation to the solar year approximately every 33 Islamic years. It is used mainly for religious purposes, but in Saudi Arabia it is the official calendar. Other lunar calendars often include extra months added occasionally to synchronize it with the solar calendar.

The oldest known lunar calendar was found in Scotland at Warren Field and dates back to around 8,000 BC.Alexander Marshack, in a controversial reading, believed that marks on a bone baton (c. 25,000 BCE) represented a lunar calendar. Similarly, Michael Rappenglueck believes that marks on a 17,000-year-old cave painting in Lascaux represent a lunar calendar.