New moon

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A simulated image of the traditionally defined new Moon: the earliest visible waxing crescent (lower right), which signals the start of a new month in many lunar and lunisolar calendars. At new moon, mostly earthlight illuminates the near side of the Moon. New Moon.jpg
A simulated image of the traditionally defined new Moon: the earliest visible waxing crescent (lower right), which signals the start of a new month in many lunar and lunisolar calendars. At new moon, mostly earthlight illuminates the near side of the Moon.

In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. [2] At this phase, the lunar disk is not visible to the unaided eye, but its presence may be detected because it occults stars behind it.

Contents

The original meaning of the term 'new moon', which is still sometimes used in calendrical, non-astronomical contexts, is the first visible crescent of the Moon after conjunction with the Sun. [3] This thin waxing crescent is briefly and faintly visible as the Moon gets lower in the western sky after sunset. The precise time and even the date of the appearance of the new moon by this definition will be influenced by the geographical location of the observer. The first crescent marks the beginning of the month in the Islamic calendar [4] and in some lunisolar calendars such as the Hebrew calendar. In the Chinese calendar, the beginning of the month is marked by the dark moon, the last visible crescent of a waning Moon.

The astronomical new moon, sometimes known as the dark moon to avoid confusion, occurs by definition at the moment of conjunction in ecliptical longitude with the Sun, when the Moon is invisible from the Earth. This moment is unique and does not depend on location, and in certain circumstances it coincides with a solar eclipse.

A lunation, or synodic month, is the time period from one new moon to the next. In the J2000.0 epoch, the average length of a lunation is 29.53059 days (or 29 days, 12 hours, 44 minutes, and 3 seconds). [5] 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. [6]

Lunation number

The Lunation Number or Lunation Cycle is a number given to each lunation beginning from a certain one in history. Several conventions are in use. [7]

The most commonly used was the Brown Lunation Number (BLN), which defines lunation 1 as beginning at the first new moon of 1923, the year when Ernest William Brown's lunar theory was introduced in the American Ephemeris and Nautical Almanac.[ citation needed ] Lunation 1 occurred at approximately 02:41 UTC, January 17, 1923. With later refinements, the BLN was used in almanacs until 1983. [8]

A more recent lunation number (simply called the Lunation Number) was introduced by Jean Meeus in 1998. [9] defines lunation 0 as beginning on the first new moon of 2000 (this occurred at approximately 18:14 UTC, January 6, 2000). The formula relating Meeus's Lunation Number with the Brown Lunation Number is: BLN = LN + 953.

The Goldstine Lunation Number refers to the lunation numbering used by Herman Goldstine, [10] with lunation 0 beginning on January 11, 1001 BCE, and can be calculated using GLN = LN + 37105.

The Hebrew Lunation Number is the count of lunations in the Hebrew calendar with lunation 1 beginning on October 7, 3761 BCE.[ citation needed ] It can be calculated using HLN = LN + 71234.

The Islamic Lunation Number is the count of lunations in the Islamic Calendar with lunation 1 as beginning on first day of the month of Muharram, which occurred in 622 CE (July 15, Julian, in the proleptic reckoning). [11] It can be calculated using ILN = LN + 17038.

The Thai Lunation Number is called "มาสเกณฑ์" (Maasa-Kendha), defines lunation 0 as the beginning of Burmese era of the Buddhist calendar on Sunday March 22, 638 CE.[ citation needed ] It can be calculated using TLN = LN + 16843.

Lunisolar calendars

Hebrew calendar

The new moon, in Hebrew Rosh Chodesh, signifies the start of every Jewish month, and is considered an important date and minor holiday in the Hebrew calendar. The modern form of the calendar is a rule-based lunisolar calendar, akin to the Chinese calendar, measuring months defined in lunar cycles as well as years measured in solar cycles, and distinct from the purely lunar Islamic calendar and the predominantly solar Gregorian calendar. The Jewish months are fixed to the annual seasons by setting the new moon of Aviv, the barley ripening, or spring, as the first moon and head of the year. [12] Since the Babylonian captivity, this month is called Nisan, and it is calculated based on mathematical rules designed to ensure that festivals are observed in their traditional season. Passover always falls in the springtime. [13] This fixed lunisolar calendar follows rules introduced by Hillel II and refined until the ninth century This calculation makes use of a mean lunation length used by Ptolemy and handed down from Babylonians, which is still very accurate: ca. 29.530594 days vs. a present value (see below) of 29.530589 days. This difference of only 0.000005, or five millionths of a day, adds up to about only four hours since Babylonian times.[ citation needed ]

The messianic Pentecostal group, the New Israelites of Peru, keeps the new moon as a Sabbath of rest. As an evangelical church, it follows the Bible's teachings that God sanctified the seventh-day Sabbath, and the new moons in addition to it. [14] No work may be done from dusk until dusk, and the services run for 11 hours, although a large number spend 24 hours within the gates of the temples, sleeping and singing praises throughout the night. [15]

Chinese calendar

The new moon is the beginning of the month in the Chinese calendar. Some Buddhist Chinese keep a vegetarian diet on the new moon and full moon each month. [16]

Hindu calendar

Amavasya and Prathama tithi Amavasya and Prathama tithi.jpg
Amavasya and Prathama tithi

The new moon is significant in the lunar Hindu calendar. The first day of the calendar starts the day after the dark moon phase (Amavasya).[ citation needed ]

There are fifteen moon dates for each of the waxing and waning periods. These fifteen dates divided evenly into five categories: Nanda, Bhadra', Jaya, Rikta, and Purna, which are cycled through in that order.[ citation needed ]

Babylonian calendar

Lunar calendars

Islamic calendar

The lunar Hijri calendar has exactly 12 lunar months in a year of 354 or 355 days. [17] It has retained an observational definition of the new moon, marking the new month when the first crescent moon is actually seen, and making it impossible to be certain in advance of when a specific month will begin (in particular, the exact date on which the month of Ramadan will begin is not known in advance). In Saudi Arabia, the new King Abdullah Centre for Crescent Observations and Astronomy in Mecca has a clock for addressing this as an international scientific project. [ citation needed ] In Pakistan, there is a "Central Ruet-e-Hilal Committee" whose head is Mufti Muneeb-ur-Rehman, assisted by 150 observatories of the Pakistan Meteorological Department, which announces the sighting of the new moon. [18]

An attempt to unify Muslims on a scientifically calculated worldwide calendar was adopted by both the Fiqh Council of North America and the European Council for Fatwa and Research in 2007. The new calculation requires that conjunction must occur before sunset in Mecca, Saudi Arabia, and that, in the same evening, moonset must take place after sunset. These can be precisely calculated and therefore a unified calendar is possible should it become adopted worldwide. [19] [20]

Solar calendars holding moveable feasts

Baháʼí calendar

The Baháʼí calendar is a solar calendar with certain new moons observed as moveable feasts. In the Baháʼí Faith, effective from 2015 onwards, the "Twin Holy Birthdays", referring to two successive holy days in the Baháʼí calendar (the birth of the Báb and the birth of Bahá'u'lláh), will be observed on the first and the second day following the occurrence of the eighth new moon after Naw-Rúz (Baháʼí New Year), as determined in advance by astronomical tables using Tehran as the point of reference. [21] This will result in the observance of the Twin Birthdays moving, year to year, from mid-October to mid-November according to the Gregorian calendar. [22]

Christian liturgical calendar

Easter, the most important feast in the Christian liturgical calendar, is a movable feast. The date of Easter is determined by reference to the ecclesiastical full moon, which, being historically difficult to determine with precision, is defined as being fourteen days after the (first crescent) new moon. [23] [24]

See also

Notes

    1. Planetlight, zodiacal light, and starlight contribute a negligible amount of the total light that the lunar surface reflects.

    Related Research Articles

    Calendar System for organizing the days of year

    A calendar is a system of organizing days. 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 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.

    Full moon Lunar phase: completely illuminated disc

    The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon. This means that the lunar hemisphere facing Earth – the near side – is completely sunlit and appears as a circular disk. The full moon occurs roughly once a month.

    Islamic calendar Lunar calendar used by Muslims to determine religious observances

    The Hijri calendar, also known as the Lunar Hijri calendar and as the Islamic, Muslim or Arabic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to determine the proper days of Islamic holidays and rituals, such as the annual period of fasting and the proper time for the Hajj. In almost all countries where the predominant religion is Islam, the civil calendar is the Gregorian calendar, with Syriac month-names used in the Levant and Mesopotamia. Notable exceptions to this rule are Iran and Afghanistan, which use the Solar Hijri calendar. Rents, wages and similar regular commitments are generally paid by the civil calendar.

    Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendars may require intercalations of both days and months.

    A leap year is a calendar year that contains an additional day added to keep the calendar year synchronized with the astronomical year or seasonal year. Because astronomical events and seasons do not repeat in a whole number of days, calendars that have a constant number of days in each year will unavoidably drift over time with respect to the event that the year is supposed to track, such as seasons. By inserting an additional day or month into some years, the drift between a civilization's dating system and the physical properties of the Solar System can be corrected. A year that is not a leap year is a common year.

    Lunar calendar Calendar based on the phases of the Moon

    A lunar calendar is a calendar based on the monthly cycles of the Moon's phases, in contrast to solar calendars, whose annual cycles are based only directly on the solar year. The most commonly used calendar, the Gregorian calendar, is a solar calendar system that originally evolved out of a lunar calendar system. A purely lunar calendar is also distinguished from a lunisolar calendar, whose lunar months are brought into alignment with the solar year through some process of intercalation. The details of when months begin varies from calendar to calendar, with some using new, full, or crescent moons and others employing detailed calculations.

    Lunisolar calendar Calendar with lunar month, solar year

    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. As with all calendars which divide the year into months 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.

    A month is a unit of time, used with calendars, that is approximately as long as a natural orbital period of the Moon; the words month and Moon are cognates. The traditional concept arose with the cycle of Moon phases; such lunar months ("lunations") are synodic months and last approximately 29.53 days. From excavated tally sticks, researchers have deduced that people counted days in relation to the Moon's phases as early as the Paleolithic age. Synodic months, based on the Moon's orbital period with respect to the Earth-Sun line, are still the basis of many calendars today, and are used to divide the year

    Lunar phase Shape of the Moons directly sunlit portion as viewed from Earth

    The lunar phase or Moon phase is the shape of the Moon's directly sunlit portion as viewed from Earth. The lunar phases gradually change over a synodic month as the Moon's orbital positions around Earth and Earth around the Sun shift. The visible side of the moon is variously sunlit, depending on the position of the Moon in its orbit. Thus, this face's sunlit portion can vary from 0% to 100% . Each of the four "intermediate" lunar phases is approximately 7.4 days, with slight variation due to the Moon's orbit's elliptical shape.

    Metonic cycle Span of 235 lunar months close to 19 solar years

    The Metonic cycle or enneadecaeteris is a period of approximately 19 years after which the phases of the moon recur at the same time of the year. The recurrence is not perfect, and by precise observation the Metonic cycle defined as 235 synodic lunar months is just 1 hour, 27 minutes and 33 seconds longer than 19 tropical years. Meton of Athens, in the 5th century BC, judged the cycle to be a whole number of days, 6,940. Using these whole numbers facilitates the construction of a lunisolar calendar.

    A moveable feast or movable feast is an observance in a Christian liturgical calendar, borrowed from the Hebrew Lunisolar calendar, which therefore occurs on a different date in different years.

    A solar calendar is a calendar whose dates indicate the season or almost equivalently the apparent position of the Sun relative to the stars. The Gregorian calendar, widely accepted as a standard in the world, is an example of a solar calendar. The main other type of calendar is a lunar calendar, whose months correspond to cycles of Moon phases. The months of the Gregorian calendar do not correspond to cycles of the Moon phase.

    Date of Easter Calculation of the date of Easter

    As a moveable feast, the date of Easter is determined in each year through a calculation known as computus. Easter is celebrated on the first Sunday after the Paschal full moon, which is the first full moon on or after 21 March. Determining this date in advance requires a correlation between the lunar months and the solar year, while also accounting for the month, date, and weekday of the Julian or Gregorian calendar. The complexity of the algorithm arises because of the desire to associate the date of Easter with the date of the Jewish feast of Passover which, Christians believe, is when Jesus was crucified.

    Calendar reform or calendrical reform is any significant revision of a calendar system. The term sometimes is used instead for a proposal to switch to a different calendar design.

    Babylonian calendar

    The Babylonian calendar was a lunisolar calendar with years consisting of 12 lunar months, each beginning when a new crescent moon was first sighted low on the western horizon at sunset, plus an intercalary month inserted as needed by decree. The calendar is based on a Sumerian predecessor preserved in the Umma calendar of Shulgi.

    The Tabular Islamic calendar is a rule-based variation of the Islamic calendar. It has the same numbering of years and months, but the months are determined by arithmetical rules rather than by observation or astronomical calculations. It was developed by early Muslim astronomers of the second hijra century to provide a predictable time base for calculating the positions of the moon, sun, and planets. It is now used by historians to convert an Islamic date into a Western calendar when no other information is available. Its calendar era is the Hijri year.

    The Islamic New Year, also called the Hijri New Year or Arabic New Year, is the day that marks the beginning of a new lunar Hijri year, and is the day on which the year count is incremented. The first day of the Islamic year is observed by most Muslims on the first day of the month of Muharram. The epoch of the Islamic era was set as 622 Common Era (CE), the year of the emigration of Muhammad and his followers from Mecca to Medina, known as the Hijra. All religious duties, such as prayer, fasting in the month of Ramadan, and pilgrimage, and the dates of significant events, such as celebration of holy nights and festivals, are calculated according to the Islamic calendar.

    The Hijri year or era is the era used in the Islamic lunar calendar, which begins its count from the Islamic New Year in 622 CE. During that year, Muhammad and his followers migrated from Mecca to Yathrib. This event, known as the Hijra, is commemorated in Islam for its role in the founding of the first Muslim community (ummah).

    Molad is a Hebrew word meaning "birth" that also generically refers to the time at which the New Moon is "born". The word is ambiguous, however, because depending on the context it could refer to the actual or mean astronomical lunar conjunction, or the molad of the traditional Hebrew calendar, or at a specified locale the first visibility of the new lunar crescent after a lunar conjunction.

    Lunar month Time between successive new moons

    In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month.

    References

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    12. Exodus 12:1–2
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    24. Dershowitz & Reingold 2008, pp. 114–115.

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