HOME

TheInfoList



OR:

In
lunar calendar A lunar calendar is a calendar based on the monthly cycles of the Moon's phases ( synodic months, lunations), in contrast to solar calendars, whose annual cycles are based only directly on the solar year. The most commonly used calendar, t ...
s, a lunar month is the time between two successive syzygies of the same type:
new moon In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the naked eye, except when it is silhouetted against the Sun during a solar ecl ...
s or
full moon 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 (when the ecliptic longitudes of the Sun and Moon differ by 180°). This mea ...
s. The precise definition varies, especially for the beginning of the month.


Variations

In Shona,
Middle East The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabian Peninsula, Arabia (including the Arabian Peninsula and Bahrain), Anatolia, Asia Minor (Asian part of Turkey except Hatay Pro ...
ern, and
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
an traditions, the month starts when the young crescent moon first becomes visible, at evening, after
conjunction Conjunction may refer to: * Conjunction (grammar), a part of speech * Logical conjunction, a mathematical operator ** Conjunction introduction, a rule of inference of propositional logic * Conjunction (astronomy), in which two astronomical bodies ...
with the Sun one or two days before that evening (e.g., in the
Islamic calendar The Hijri calendar ( ar, ٱلتَّقْوِيم ٱلْهِجْرِيّ, translit=al-taqwīm al-hijrī), also known in English as the Muslim calendar and Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 ...
). In ancient Egypt, the lunar month began on the day when the waning moon could no longer be seen just before sunrise. Others run from
full moon 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 (when the ecliptic longitudes of the Sun and Moon differ by 180°). This mea ...
to full moon. Yet others use calculation, of varying degrees of sophistication, for example, the
Hebrew calendar The Hebrew calendar ( he, הַלּוּחַ הָעִבְרִי, translit=HaLuah HaIvri), also called the Jewish calendar, is a lunisolar calendar used today for Jewish religious observance, and as an official calendar of the state of Israel ...
or the ecclesiastical lunar calendar. Calendars count integer days, so months may be 29 or 30 days in length, in some regular or irregular sequence.
Lunar cycles Concerning the lunar month of ~29.53 days as viewed from Earth, the lunar phase or Moon phase is the shape of the Moon's directly sunlit portion, which can be expressed quantitatively using areas or angles, or described qualitatively using the t ...
are prominent, and calculated with great precision, in the ancient Hindu
Panchangam A panchāngam ( sa, पञ्चाङ्गम्; ) is a Hindu calendar and almanac, which follows traditional units of Hindu timekeeping, and presents important dates and their calculations in a tabulated form. It is sometimes spelled ''Pa ...
calendar, widely used in the Indian subcontinent. In India, the month from conjunction to conjunction is divided into thirty parts known as . A is between 19 and 26 hours long. The date is named after the ruling at sunrise. When the is shorter than the day, the may jump. This case is called or . Conversely a may 'stall' as well, that is – the same is associated with two consecutive days. This is known as . In English
common law In law, common law (also known as judicial precedent, judge-made law, or case law) is the body of law created by judges and similar quasi-judicial tribunals by virtue of being stated in written opinions."The common law is not a brooding omniprese ...
, a "lunar month" traditionally meant exactly 28 days or four weeks, thus a contract for 12 months ran for exactly 48 weeks. In the United Kingdom, the lunar month was formally replaced by the
calendar month 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 and specific day within such a system. A calendar is also a physi ...
for deeds and other written contracts by section 61(a) of the
Law of Property Act 1925 The Law of Property Act 1925c 20 is a statute of the United Kingdom Parliament. It forms part of an interrelated programme of legislation introduced by Lord Chancellor Lord Birkenhead between 1922 and 1925. The programme was intended to modern ...
and for post-1850 legislation by the
Interpretation Act 1978 The Interpretation Act 1978 is an Act of the Parliament of the United Kingdom. The Act makes provision for the interpretation of Acts of Parliament, Measures of the General Synod of the Church of England, Measures of the Church Assembly, subor ...
(Schedule 1 read with sections 5 and 23 and with Schedule 2 paragraph 4(1)(a)) and its predecessors.


Types

There are several types of lunar month. The term ''lunar month'' usually refers to the synodic month because it is the cycle of the visible
phases of the Moon Concerning the lunar month of ~29.53 days as viewed from Earth, the lunar phase or Moon phase is the shape of the Moon's directly sunlit portion, which can be expressed quantitatively using areas or angles, or described qualitatively using the t ...
. Most of the following types of lunar month, except the distinction between the sidereal and tropical months, were first recognized in Babylonian lunar astronomy.


Sidereal month

The period of the
Moon's orbit The Moon orbits Earth in the retrograde and prograde motion, prograde direction and completes one orbital period, revolution relative to the March Equinox, Vernal Equinox and the fixed stars, stars in about 27.32 days (a tropical month and sider ...
as defined with respect to the
celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphe ...
of apparently
fixed stars In astronomy, fixed stars ( la, stellae fixae) is a term to name the full set of glowing points, astronomical objects actually and mainly stars, that appear not to move relative to one another against the darkness of the night sky in the backgro ...
(the
International Celestial Reference Frame The International Celestial Reference System (ICRS) is the current standard celestial reference system adopted by the International Astronomical Union (IAU). Its origin is at the barycenter of the Solar System, with axes that are intended to "sho ...
; ICRF) is known as a sidereal month because it is the time it takes the Moon to return to a similar position among the
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s ( la, sidera): days (27 d 7 h 43 min 11.6 s). This type of month has been observed among cultures in the Middle East, India, and China in the following way: they divided the sky into 27 or 28 lunar mansions, one for each day of the month, identified by the prominent star(s) in them.


Synodic month

The synodic month ( el, συνοδικός, translit=synodikós, meaning "pertaining to a synod, i.e., a meeting"; in this case, of the Sun and the Moon), also lunation, is the average period of the Moon's orbit with respect to the line joining the Sun and Earth: 29 d 12 h 44 min and 2.9 s. This is the period of the
lunar phase Concerning the lunar month of ~29.53 days as viewed from Earth, the lunar phase or Moon phase is the shape of the Moon's directly sunlit portion, which can be expressed quantitatively using areas or angles, or described qualitatively using the t ...
s, because the Moon's appearance depends on the position of the Moon with respect to the Sun as seen from Earth. While the Moon is orbiting Earth, Earth is progressing in its orbit around the Sun. After completing a sidereal month, the Moon must move a little further to reach the new position having the same angular distance from the Sun, appearing to move with respect to the stars since the previous month. Therefore, the synodic month takes 2.2 days longer than the sidereal month. Thus, about 13.37 sidereal months, but about 12.37 synodic months, occur in a
Gregorian year Gregorian may refer to: *The thought or ideology of Pope Gregory I or Pope Gregory VII (also called ''Gregorianism'') *Things named for Pope Gregory I: **Gregorian chant, the central tradition of Western plainchant, a form of monophonic, unaccom ...
. Since
Earth's orbit Earth orbits the Sun at an average distance of 149.60 million km (92.96 million mi) in a counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes  days (1 sidereal year), during which time Earth ...
around the Sun is elliptical and not
circular Circular may refer to: * The shape of a circle * ''Circular'' (album), a 2006 album by Spanish singer Vega * Circular letter (disambiguation) ** Flyer (pamphlet), a form of advertisement * Circular reasoning, a type of logical fallacy * Circular ...
, the
speed In everyday use and in kinematics, the speed (commonly referred to as ''v'') of an object is the magnitude of the change of its position over time or the magnitude of the change of its position per unit of time; it is thus a scalar quant ...
of Earth's progression around the Sun varies during the year. Thus, the angular rate is faster nearer
periapsis An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any elli ...
and slower near
apoapsis An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any elli ...
. The same is so for the Moon's orbit around Earth. Because of these variations in angular rate, the actual time between
lunation 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. Variations In Shona, Middle Eastern, and ...
s may vary from about 29.18 to about 29.93 days. The average duration in modern times is 29.53059 days with up to seven hours variation about the mean in any given year. A more precise figure may be derived for a specific synodic month using the
lunar theory Lunar theory attempts to account for the motions of the Moon. There are many small variations (or perturbations) in the Moon's motion, and many attempts have been made to account for them. After centuries of being problematic, lunar motion can now ...
of Chapront-Touzé and Chapront (1988):
where and is the
Julian day number The Julian day is the continuous count of days since the beginning of the Julian period, and is used primarily by astronomers, and in software for easily calculating elapsed days between two events (e.g. food production date and sell by date). ...
(and JD=2451545 corresponds to 1 January, AD 2000). The duration of synodic months in ancient and medieval history is itself a topic of scholarly study.


Tropical month

It is customary to specify positions of celestial bodies with respect to the March
equinox A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" and se ...
. Because of Earth's
precession of the equinoxes In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In partic ...
, this point moves back slowly along the
ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agains ...
. Therefore, it takes the Moon less time to return to an
ecliptic longitude The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System b ...
of 0° than to the same point amid the
fixed stars In astronomy, fixed stars ( la, stellae fixae) is a term to name the full set of glowing points, astronomical objects actually and mainly stars, that appear not to move relative to one another against the darkness of the night sky in the backgro ...
. This slightly shorter period, days (27 d 7 h 43 min 4.7 s), is known as the tropical month by analogy with Earth's
tropical year A tropical year or solar year (or tropical period) is the time that the Sun takes to return to the same position in the sky of a celestial body of the Solar System such as the Earth, completing a full cycle of seasons; for example, the time ...
.


Anomalistic month

The
Moon's orbit The Moon orbits Earth in the retrograde and prograde motion, prograde direction and completes one orbital period, revolution relative to the March Equinox, Vernal Equinox and the fixed stars, stars in about 27.32 days (a tropical month and sider ...
approximates an ellipse rather than a circle. However, the orientation (as well as the shape) of this orbit is not fixed. In particular, the position of the extreme points (the line of the
apsides An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ellip ...
:
perigee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any el ...
and
apogee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any el ...
), rotates once ( apsidal precession) in about 3,233 days (8.85 years). It takes the Moon longer to return to the same apsis because it has moved ahead during one revolution. This longer period is called the anomalistic month and has an average length of  days (27 d 13 h 18 min 33.2 s). The
apparent diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it ...
of the Moon varies with this period, so this type has some relevance for the prediction of
eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three c ...
s (see Saros), whose extent, duration, and appearance (whether total or annular) depend on the exact apparent diameter of the Moon. The apparent diameter of the
full moon 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 (when the ecliptic longitudes of the Sun and Moon differ by 180°). This mea ...
varies with the full moon cycle, which is the beat period of the synodic and anomalistic month, as well as the period after which the apsides point to the Sun again. An anomalistic month is longer than a sidereal month because the perigee moves in the
same direction "Same Direction" is the third single from Hoobastank's second major studio album '' The Reason''. It was released as a single in 2004, a couple of months after the release of " The Reason" as a single. "Same Direction" reached No. 20 on the ''Bill ...
as the Moon is orbiting the Earth, one revolution in nine years. Therefore, the Moon takes a little longer to return to perigee than to return to the same star.


Draconic month

A draconic month or draconitic month is also known as a nodal month or nodical month. The name ''draconic'' refers to a mythical
dragon A dragon is a reptilian legendary creature that appears in the folklore of many cultures worldwide. Beliefs about dragons vary considerably through regions, but dragons in western cultures since the High Middle Ages have often been depicted a ...
, said to live in the
lunar node A lunar node is either of the two orbital nodes of the Moon, that is, the two points at which the orbit of the Moon intersects the ecliptic. The ''ascending'' (or ''north'') node is where the Moon moves into the northern ecliptic hemisphere ...
s and eat the Sun or Moon during an
eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three c ...
. A solar or lunar eclipse is possible only when the Moon is at or near either of the two points where its orbit crosses the ecliptic plane; i.e., the satellite is at or near either of its
orbital node An orbital node is either of the two points where an orbit intersects a plane of reference to which it is inclined. A non-inclined orbit, which is contained in the reference plane, has no nodes. Planes of reference Common planes of referen ...
s. The orbit of the Moon lies in a plane that is
inclined Incline, inclined, inclining, or inclination may refer to: *Grade (slope), the tilt, steepness, or angle from horizontal of a topographic feature (hillside, meadow, etc.) or constructed element (road, railway, field, etc.) *Slope, the tilt, steepn ...
about 5.14° with respect to the ecliptic plane. The line of intersection of these planes passes through the two points at which the Moon's orbit crosses the ecliptic plane: the ''ascending node'', where the Moon enters the Northern Celestial Hemisphere, and the ''descending node'', where the Moon moves into the
Southern Southern may refer to: Businesses * China Southern Airlines, airline based in Guangzhou, China * Southern Airways, defunct US airline * Southern Air, air cargo transportation company based in Norwalk, Connecticut, US * Southern Airways Express, M ...
. The draconic or nodical month is the average interval between two successive transits of the Moon through the same
node In general, a node is a localized swelling (a " knot") or a point of intersection (a vertex). Node may refer to: In mathematics * Vertex (graph theory), a vertex in a mathematical graph * Vertex (geometry), a point where two or more curves, line ...
. Because of the
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
exerted by the Sun's gravity on the
angular momentum In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity—the total angular momentum of a closed syst ...
of the Earth–Moon system, the plane of the Moon's orbit gradually rotates westward, which means the nodes gradually rotate around Earth. As a result, the time it takes the Moon to return to the same node is shorter than a sidereal month, lasting  days (27 d 5 h 5 min 35.8 s). The line of nodes of the Moon's orbit precesses 360° in about 6,798 days (18.6 years). A draconic month is shorter than a sidereal month because the nodes precess in the opposite direction to that in which the Moon is orbiting Earth, one rotation every 18.6 years. Therefore, the Moon returns to the same node slightly earlier than it returns to meet the same reference star.


Cycle lengths

Regardless of the culture, all lunar calendar months approximate the mean length of the synodic month, the average period the Moon takes to cycle through its phases (
new New is an adjective referring to something recently made, discovered, or created. New or NEW may refer to: Music * New, singer of K-pop group The Boyz Albums and EPs * ''New'' (album), by Paul McCartney, 2013 * ''New'' (EP), by Regurgitator, ...
, first quarter, full, last quarter) and back again: 29–30
day A day is the time period of a full rotation of the Earth with respect to the Sun. On average, this is 24 hours, 1440 minutes, or 86,400 seconds. In everyday life, the word "day" often refers to a solar day, which is the length between two ...
s. The Moon completes one orbit around Earth every 27.3 days (a sidereal month), but due to
Earth's orbit Earth orbits the Sun at an average distance of 149.60 million km (92.96 million mi) in a counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes  days (1 sidereal year), during which time Earth ...
al motion around the Sun, the Moon does not yet finish a synodic cycle until it has reached the point in its orbit where the Sun is in the same
relative position In geometry, a position or position vector, also known as location vector or radius vector, is a Euclidean vector that represents the position of a point ''P'' in space in relation to an arbitrary reference origin ''O''. Usually denoted x, r, or ...
. This table lists the average lengths of five types of astronomical lunar month, derived from Chapront, Chapront-Touzé & Francou (2002). These are not constant, so a first-order (linear) approximation of the secular change is provided. Valid for the
epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided ...
J2000.0 (1 January 2000 12:00 TT): ''Note:'' In this table, time is expressed in Ephemeris Time (more precisely
Terrestrial Time Terrestrial Time (TT) is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of Earth. For example, the Astronomical Almanac uses ...
) with days of 86,400 SI
second The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds ea ...
s. ''T'' is centuries since the epoch (2000), expressed in Julian centuries of 36,525 days. For calendrical calculations, one would probably use days measured in the time scale of
Universal Time Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle wit ...
, which follows the somewhat unpredictable rotation of the Earth, and progressively accumulates a difference with ephemeris time called ΔT ("delta-T"). Apart from the long term (millennial) drift in these values, all these periods vary continually around their mean values because of the complex orbital effects of the Sun and planets affecting its motion.


Derivation

The periods are derived from polynomial expressions for Delaunay's arguments used in
lunar theory Lunar theory attempts to account for the motions of the Moon. There are many small variations (or perturbations) in the Moon's motion, and many attempts have been made to account for them. After centuries of being problematic, lunar motion can now ...
, as listed in Table 4 of Chapront, Chapront-Touzé & Francou (2002): W1 is the ecliptic longitude of the Moon w.r.t. the fixed ICRS equinox: its period is the sidereal month. If we add the rate of precession to the sidereal angular velocity, we get the angular velocity w.r.t. the equinox of the date: its period is the tropical month, which is rarely used. ''l'' is the mean anomaly, its period is the anomalistic month. ''F'' is the argument of latitude, its period is the draconic month. ''D'' is the elongation of the Moon from the Sun, its period is the synodic month. Derivation of a period from a
polynomial In mathematics, a polynomial is an expression consisting of indeterminates (also called variables) and coefficients, that involves only the operations of addition, subtraction, multiplication, and positive-integer powers of variables. An exampl ...
for an argument ''A'' (angle): A = A_0 + (A_1\times T) + (A_2\times T^2); ''T'' in centuries (cy) is 36,525 days from epoch J2000.0. The angular velocity is the first derivative: \operatorname\!A/\operatorname\!t = A' = A_1 + (2\times A_2\times T). The period (''Q'') is the inverse of the angular velocity: Q = = = \times = \times (1 - 2\times \times T) = - (2\times \times T), ignoring higher-order terms. A1 in "/cy ; A2 in "/cy2; so the result ''Q'' is expressed in cy/" which is a very inconvenient unit. 1 revolution (rev) is 360 × 60 × 60" = 1,296,000"; to convert the unit of the velocity to revolutions/day, divide A1 by B1 = 1,296,000 × 36,525 = 47,336,400,000; C1 = B1 ÷ A1 is then the period (in days/revolution) at the epoch J2000.0. For rev/day2 divide A2 by B2 = 1,296,000 × 36,5252 = 1,728,962,010,000,000. For A_2\div (A_1\times A_1) the numerical conversion factor then becomes 2 × B1 × B1 ÷ B2 = 2 × 1,296,000. This would give a linear term in days change (of the period) per day, which is also an inconvenient unit: for change per year multiply by a factor 365.25, and for change per century multiply by a factor 36,525. C2 = 2 × 1,296,000 × 36,525 × A2 ÷ (A1 × A1). Then period ''P'' in days: P = C_1 - C_2\times T. Example for synodic month, from Delaunay's argument ''D'': D′ = 1602961601.0312 − 2 × 6.8498 × T "/cy; A1 = 1602961601.0312 "/cy; A2 = −6.8498"/cy2; C1 = 47,336,400,000 ÷ 1,602,961,601.0312 = 29.530588860986 days; C2 = 94,672,800,000 × −6.8498 ÷ (1,602,961,601.0312 × 1,602,961,601.0312) = −0.00000025238 days/cy.


See also

*
Lunisolar calendar A lunisolar calendar is a calendar in many cultures, combining lunar calendars and solar calendars. The date of Lunisolar calendars therefore indicates both the Moon phase and the time of the solar year, that is the position of the Sun in ...
*
Chinese calendar The traditional Chinese calendar (also known as the Agricultural Calendar ��曆; 农历; ''Nónglì''; 'farming calendar' Former Calendar ��曆; 旧历; ''Jiùlì'' Traditional Calendar ��曆; 老历; ''Lǎolì'', is a lunisolar calendar ...
*
Hebrew calendar The Hebrew calendar ( he, הַלּוּחַ הָעִבְרִי, translit=HaLuah HaIvri), also called the Jewish calendar, is a lunisolar calendar used today for Jewish religious observance, and as an official calendar of the state of Israel ...
*
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. Th ...
*
Hindu calendar The Hindu calendar, Panchanga () or Panjika is one of various lunisolar calendars that are traditionally used in the Indian subcontinent and Southeast Asia, with further regional variations for social and Hindu religious purposes. They adopt ...
*
Islamic calendar The Hijri calendar ( ar, ٱلتَّقْوِيم ٱلْهِجْرِيّ, translit=al-taqwīm al-hijrī), also known in English as the Muslim calendar and Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 ...
*
Tibetan calendar The Tibetan calendar (), or Tibetan lunar calendar, is a lunisolar calendar, that is, the Tibetan year is composed of either 12 or 13 lunar months, each beginning and ending with a new moon. A thirteenth month is added every two or three years ...


Notes


References

* Observer's handbook 1991, Editor Roy L. Bishop, The Royal Astronomical Society of Canada (p14) {{DEFAULTSORT:Lunar Month Units of time Month Month