Editing Lunar phase

{{short description|Shape of the Moon's sunlit portion as viewed from Earth}}
[[File:2025 Moon Phases - Northern Hemisphere - 4K.webm|thumb|300px|The lunar phases and [[libration]]s in 2025 as viewed from the [[Northern Hemisphere]] at hourly intervals, with titles and supplemental graphics]]
[[File:2025 Moon Phases - Southern Hemisphere - 4K.webm|thumb|300px|The lunar phases and [[libration]]s in 2025 as viewed from the [[Southern Hemisphere]] at hourly intervals, with titles and supplemental graphics]]
[[File:Moondrop.jpg|thumb|right|250px|A [[full moon]] sets behind [[San Gorgonio Mountain]] in California on a midsummer's morning.]]

A '''lunar phase''' or '''Moon phase''' is the apparent shape of the [[Moon]]'s directly sunlit portion as viewed from the [[Earth]]. Because the Moon is [[Tidal locking|tidally locked]] with the Earth, the same [[Hemisphere (geometry)|hemisphere]] is always facing the Earth. In common usage, the four major phases are the [[new moon]], the first quarter, the [[full moon]] and the last quarter; the four minor phases are waxing crescent, waxing gibbous, waning gibbous, and waning crescent. A [[lunar month]] is the time between successive recurrences of the same phase: due to the [[Orbital eccentricity|eccentricity]] of the Moon's orbit, this duration is not perfectly constant but averages about 29.5 days.

The appearance of the Moon (its phase) gradually changes over a lunar month as the relative orbital positions of the Moon around Earth, and Earth around the Sun, shift. The visible side of the Moon is sunlit to varying extents, depending on the position of the Moon in its orbit, with the sunlit portion varying from 0% (at new moon) to nearly 100% (at full moon).<ref>{{cite web |title=Is the 'full moon' merely a fallacy? |website=[[NBC News]] |date=28 February 2004 |url=https://www.nbcnews.com/id/wbna4402294 |access-date=2023-05-30 |language=en}}</ref>

==Phenomenon==
The Moon rotates, as it orbits Earth, changing orientation toward the Sun, experiencing a [[lunar day]]. A lunar day is equal to one [[lunar month]] (one synodic orbit around Earth) due to it being [[tidal locking|tidally locked]] to Earth. Since the Moon is not tidally locked to the Sun, lunar daylight and night times both occur around the Moon. The changing position of the illumination of the Moon by the Sun during a lunar day is observable from Earth as the changing lunar phases, waxing crescent being the sunrise and the waning crescent the sunset phase of a day observed from afar.<ref name="r040">{{cite web | title=Phases of the Moon explained | website=BBC Sky at Night Magazine | date=January 21, 2025 | url=https://www.skyatnightmagazine.com/space-science/why-does-the-moons-appearance-change | access-date=April 29, 2025}}</ref>

==Phases of the Moon==
{{Redirect|Waxing gibbous|the album|Waxing Gibbous}}
{{Redirect|Last quarter|the manga series|Last Quarter}}
[[File:Moon phases en.jpg|450px|thumb|left|The phases of the Moon as viewed looking southward from the [[Northern Hemisphere]]. Each phase would be rotated 180° if seen looking northward from the [[Southern Hemisphere]]. The upper part of the diagram is not to scale, as the Moon, the  Earth, and the Moon's orbit are all much smaller relative to the Earth's orbit than shown here.]]

There are four ''principal'' (primary, or major) lunar phases: the [[new moon]], first quarter, [[full moon]], and last quarter (also known as third or final quarter), when the Moon's [[ecliptic longitude]] is at an angle to the Sun (as viewed from the center of the Earth) of 0°, 90°, 180°, and 270° respectively.{{sfn|Seidelmann|1992|p=478}}{{efn|The quarter phases happen when the observer–Moon–Sun angle is 90°{{citation needed|date=December 2022}}, also known as [[quadrature (astronomy)| quadrature]]{{dubious|date=December 2022}}. This is not the same as a [[right angle]]{{dubious|date=December 2022|reason=a right angle is definitely 90°. An observer–Moon–Sun angle of 90° is [[dichotomy]] not quadrature. [[Quadrature (astronomy)]] is when the sun-observer-moon angle is 90°. Also this contradicts the next section which says a quarter moon starts at 50.1% lit, while this description of dichotomy is describing the moon as exactly 50% lit}}, but the difference is very slight. /}} Each of these phases appears at slightly different times at different locations on Earth, and tabulated times are therefore always ''geocentric'' (calculated for the Earth's center).

Between the principal phases are ''intermediate'' phases, during which the apparent shape of the illuminated Moon is either [[crescent]] or [[wikt: gibbous|gibbous]]. On average, the intermediate phases last one-quarter of a [[synodic month]], or 7.38 days.{{efn|Their durations [[orbital eccentricity |vary slightly]] because the [[orbit of the Moon| Moon's orbit]] is somewhat [[elliptic orbit| elliptical]], so its [[orbital speed]] is not constant.}}

The term ''{{linktext|waxing}}'' is used for an intermediate phase when the Moon's apparent shape is thickening, from new to a full moon; and ''{{linktext|waning}}'' when the shape is thinning. The duration from full moon to new moon (or new moon to full moon) varies from approximately {{nowrap|13 days {{frac|22|1|2}} hours}} to about {{nowrap|15 days {{frac|14|1|2}} hours}}.

Due to lunar motion relative to the meridian and the [[ecliptic]], in Earth's [[northern hemisphere]]:
*A new moon appears highest at the summer [[solstice]] and lowest at the winter solstice.
*A first-quarter moon appears highest at the spring [[equinox]] and lowest at the autumn equinox.
*A full moon appears highest at the winter solstice and lowest at the summer solstice.
*A last-quarter moon appears highest at the autumn equinox and lowest at the spring equinox.

Non-Western cultures may use a different number of lunar phases; for example, traditional [[Hawaiian culture]] has a total of 30 phases (one per day).<ref>
{{cite web |title=Hawaiian Moon Names |url=http://www.imiloahawaii.org/57/ |url-status=dead |archive-url= https://web.archive.org/web/20140102085746/http://www.imiloahawaii.org/57 |archive-date= 2014-01-02 |access-date=2013-07-08 |work=Imiloa, Hilo Attractions |language=en}}</ref>
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=== Waxing and waning ===
[[File:The Moon's Phases as Seen from Space.ogv|thumb|left|This video provides an illustration of how the Moon passes through its phases &ndash; a product of its orbit, which allows different parts of its surface to be illuminated by the Sun over the course of a month. The camera is locked to the Moon as Earth rapidly rotates in the foreground.]]
[[File:Moon Phase Diagram for Simple English Wikipedia.GIF|thumb|right|Diagram of the Moon's phases: The Earth is at the center of the diagram and the Moon is shown orbiting.]]
When the Sun and Moon are [[conjunction (astronomy)|aligned on the same side]] of the Earth (conjunct), the Moon is "new", and the side of the Moon facing Earth is not illuminated by the Sun. As the Moon ''waxes'' (the amount of illuminated surface as seen from Earth increases), the lunar phases progress through the new moon, crescent moon, first-quarter moon, [[wikt:gibbous|gibbous]] moon, and full moon phases. The Moon then ''wanes'' as it passes through the gibbous moon, third-quarter moon, and crescent moon phases, before returning back to new moon.

The terms ''old moon'' and ''new moon'' are not interchangeable. The "old moon" is a waning sliver (which eventually becomes undetectable to the naked eye) until the moment it aligns with the Sun and begins to wax, at which point it becomes new again.<ref>{{cite web |title=Free Astronomy Lesson 7 - The Phases of the Moon |url=http://www.synapses.co.uk/astro/moon2.html |access-date=2015-12-28 |archive-url=https://web.archive.org/web/20230414073024/http://www.synapses.co.uk/astro/moon2.html |archive-date=2023-04-14 |url-status=live}}</ref> ''Half moon'' is often used to mean the first- and third-quarter moons, while the term ''quarter'' refers to the extent of the Moon's cycle around the Earth, not its shape.

When an illuminated hemisphere is viewed from a certain angle, the portion of the illuminated area that is visible will have a two-dimensional shape as defined by the intersection of an [[ellipse]] and circle (in which the ellipse's [[major axis]] coincides with the circle's diameter). If the half-ellipse is convex with respect to the half-circle, then the shape will be gibbous (bulging outwards),<ref>{{cite web |title=Gibbous Definition & Meaning |url=https://www.dictionary.com/browse/gibbous |website=[[Dictionary.com]] |archive-url=https://web.archive.org/web/20230421145830/https://www.dictionary.com/browse/gibbous |archive-date=2023-04-21 |language=en |quote=Origin of gibbous: 1350–1400; Middle English <Latin gibbōsus humped, equivalent to gibb(a) hump + -ōsus-ous |url-status=live}}</ref> whereas if the half-ellipse is concave with respect to the half-circle, then the shape will be a [[crescent]]. When a crescent moon occurs, the phenomenon of [[earthlight (astronomy)|earthshine]] may be apparent, where the night side of the Moon dimly reflects indirect sunlight reflected from Earth.{{sfn|Asmelash|Allan|2019|}}
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=== Principal and intermediate phases of the Moon ===
{|class="wikitable"
|-
!scope="col" rowspan="2" colspan="2"| Moon phases
!scope="col" colspan="2"| Illuminated portion
!scope="col" rowspan="2"| Visibility
!scope="col" rowspan="2"| Average<br /> moonrise<br /> time{{efn|name=rise|As with sunrise and sunset, there are seasonal variations in the time of moonrise and moonset.}}
!scope="col" rowspan="2"| [[Culmination]]<br /> time<br /> (highest point)
!scope="col" rowspan="2"| Average<br /> moonset<br /> time{{efn|name=rise}}
!scope="col" colspan="2"| Illustrations from
!scope="col" rowspan="2"| Photograph<br /> (view from the<br /> Northern Hemisphere)
|-
!scope="col"| [[Northern Hemisphere|Northern<br /> Hemisphere]]
!scope="col"| [[Southern Hemisphere|Southern<br /> Hemisphere]]
!scope="col"| [[North Pole|North<br /> Pole]]
!scope="col"| [[South Pole|South<br /> Pole]]
|-id="newmoon"
!scope="row" colspan="2"| [[New Moon]]
|colspan="2" style="text-align:center"| Disc completely in shade<br /> (lit by [[earthshine]] only)
| Invisible (too close to Sun),<br /> except during a total or annular [[solar eclipse]]<br />(when the Moon obscures the Sun disc)
|style="text-align:center"| 06:00 ||style="text-align:center"| 12:00 ||style="text-align:center"| 18:00
|colspan="2" style="text-align:center"| [[File:Moon phase 0.svg|70px]]
|style="text-align:center"| [[File:New Moon.jpg|150px]]
|-id="waxingcrescent"
!scope="row" rowspan="3"| Waxing<br /> moon
!scope="row"| Waxing<br/> [[crescent]]
| Right side:<br /> (1%–49%) lit disc || Left side:<br /> (1%–49%) lit disc
| Late morning to post-dusk
|style="text-align:center"| 09:00 ||style="text-align:center"| 15:00 ||style="text-align:center"| 21:00
|style="text-align:center"| [[File:Moon phase 1.svg|70px]]
|style="text-align:center"| [[File:Moon phase 7.svg|70px]]
|style="text-align:center"| [[File:Waxing Crescent Moon on 4-1-17 (33627493622).jpg|150px]]
|-id="firstquarter"
!scope="row"| First<br/> quarter
| Right side:<br /> 50% lit disc || Left side:<br /> 50% lit disc
| Afternoon and early night
|style="text-align:center"| 12:00 ||style="text-align:center"| 18:00 ||style="text-align:center"| 00:00
|style="text-align:center"| [[File:Moon phase 2.svg|70px]]
|style="text-align:center"| [[File:Moon phase 6.svg|70px]]
|style="text-align:center"| [[File:Daniel Hershman - march moon (by).jpg|150px]]
|-id="waxinggibbous"
!scope="row"| Waxing<br/> gibbous
| Right side:<br /> (51%–99%) lit disc || Left side:<br /> (51%–99%) lit disc
| Late afternoon and most of night
|style="text-align:center"| 15:00 ||style="text-align:center"| 21:00 ||style="text-align:center"| 03:00
|style="text-align:center"| [[File:Moon phase 3.svg|70px]]
|style="text-align:center"| [[File:Moon phase 5.svg|70px]]
|style="text-align:center"| [[File:Lune-Nikon-600-F4 Luc Viatour.jpg|150px]]
|-id="fullmoon"
!scope="row" colspan="2"| [[Full Moon]]
|colspan="2" style="text-align:center"| 100% illuminated disc,<br /> except during a total or partial [[lunar eclipse]]<br />(when the Moon crosses the Earth's shadow)
| Sunset to sunrise (all night)
|style="text-align:center"| 18:00 ||style="text-align:center"| 00:00 ||style="text-align:center"| 06:00
|colspan="2" style="text-align:center"| [[File:Moon phase 4.svg|70px]]
|style="text-align:center"| [[File:20110319 Supermoon.jpg|150px]]
|-id="waninggibbous"
!scope="row" rowspan="3"| Waning<br /> moon
!scope="row"| Waning<br/> gibbous
| Left side:<br /> (99%–51%) lit disc || Right side:<br /> (99%–51%) lit disc
| Most of night and early morning
|style="text-align:center"| 21:00 ||style="text-align:center"| 03:00 ||style="text-align:center"| 09:00
|style="text-align:center"| [[File:Moon phase 5.svg|70px]]
|style="text-align:center"| [[File:Moon phase 3.svg|70px]]
|style="text-align:center"| [[File:2013-01-02 00-00-55-Waning-gibbous-moon.jpg|150px]]
|-id="lastquarter"
!scope="row"| Last<br/> quarter
| Left side:<br /> 50% lit disc || Right side:<br /> 50% lit disc
| Late night and morning
|style="text-align:center"| 00:00 ||style="text-align:center"| 06:00 ||style="text-align:center"| 12:00
|style="text-align:center"| [[File:Moon phase 6.svg|70px]]
|style="text-align:center"| [[File:Moon phase 2.svg|70px]]
|style="text-align:center"| [[File:Waning gibbous moon near last quarter - 23 Sept. 2016.png|150px]]
|-id="waningcrescent"
!scope="row"| Waning<br/> crescent
| Left side:<br /> (49%–1%) lit disc || Right side:<br /> (49%–1%) lit disc
| Pre-dawn to early afternoon
|style="text-align:center"| 03:00 ||style="text-align:center"| 09:00 ||style="text-align:center"| 15:00
|style="text-align:center"| [[File:Moon phase 7.svg|70px]]
|style="text-align:center"| [[File:Moon phase 1.svg|70px]]
|style="text-align:center"| [[File:Waning Crescent Moon(7Sep15).jpg|150px]]
|}

==Timekeeping <span class="anchor" id="Calendar"></span> ==
{{main|Lunar calendar|Lunisolar calendar|Metonic cycle|Intercalation (timekeeping){{!}}Intercalation|History of calendars}}
Archaeologists have reconstructed methods of [[timekeeping]] that go back to prehistoric times, at least as old as the [[Neolithic]]. The natural units for timekeeping used by most historical societies are the [[day]], the [[solar year]] and the [[lunation]]. The first crescent of the new moon provides a clear and regular marker in time and pure lunar calendars (such as the Islamic [[Islamic calendar|Hijri calendar]]) rely completely on this metric. The fact, however, that a year of twelve lunar months is ten or eleven days shorter than the solar year means that a lunar calendar drifts out of step with the seasons. Lunisolar calendars resolve this issue with a year of thirteen lunar months every few years, or by restarting the count at the first new (or full) moon after the [[winter solstice]]. The [[Sumerian calendar]] is the first recorded to have used the former method; [[Chinese calendar]] uses the latter, despite delaying its start [[Chinese New Year#Dates in Chinese lunisolar calendar|until the second or even third new moon]] after the solstice. The [[Hindu calendar]], also a lunisolar calendar, further divides the month into [[Astronomical basis of the Hindu calendar|two fourteen day periods]] that mark the waxing moon and the waning moon. 

The ancient [[Roman calendar]] was broadly a lunisolar one; on the decree of [[Julius Caesar]] in the first century BCE, Rome changed to a [[solar calendar]] of twelve months, each of a fixed number of days except in a [[leap year]]. This, the [[Julian calendar]] (slightly revised in 1582 to correct the [[leap year]] rule), is the basis for the [[Gregorian calendar]] that is almost exclusively the [[civil calendar]] in use worldwide today.

==Calculating phase==
[[File:BethinAZ - 10-13.002 (by).jpg|thumb|right|220px|A crescent Moon over [[Kingman, Arizona]]]]

Each of the four intermediate phases lasts approximately seven days (7.38 days on average), but varies ±11.25% due to lunar [[apsis|apogee and perigee]].

The number of days counted from the time of the [[new moon]] is the Moon's "age". Each complete cycle of phases is called a "[[lunation]]".<ref>{{cite web |url=http://aa.usno.navy.mil/faq/docs/moon_phases.php |title=Phases of the Moon and Percent of the Moon Illuminated |website=aa.usno.navy.mil |language=en |access-date=2018-02-12 |archive-date=2018-02-06 |archive-url=https://web.archive.org/web/20180206063503/http://aa.usno.navy.mil/faq/docs/moon_phases.php |url-status=dead }}</ref>

The approximate age of the Moon, and hence the approximate phase, can be calculated for any date by calculating the number of days since a known new moon (such as 1 January 1900 or 11 August 1999) and reducing this [[modulo operation|modulo]] 29.53059 days (the mean length of a [[synodic month]]).{{sfn|Seidelmann|1992|p=577}}{{efn|Lunar months vary in length about the mean by up to seven hours in any given year. In 2001, the synodic months varied from 29d 19h 14m in January to 29d 07h 11m in July.<ref>{{cite web | title=Length of the Synodic Month: 2001 to 2100 | website=astropixels.com |date=8 November 2019 |url=http://astropixels.com/ephemeris/moon/synodicmonth2001.html}}</ref>}} The difference between two dates can be calculated by subtracting the [[Julian day|Julian day number]] of one from that of the other, or there are simpler formulae giving (for instance) the number of days since 31 December 1899. However, this calculation assumes a perfectly [[circular orbit]] and makes no allowance for the time of day at which the new moon occurred and therefore may be incorrect by several hours. (It also becomes less accurate the larger the difference between the required date and the reference date.) It is accurate enough to use in a novelty clock application showing lunar phase, but specialist usage taking account of lunar apogee and perigee requires a more elaborate calculation. Also, due to [[lunar libration]] it is not uncommon to see up to 101% of the full moon  or even up to 5% of the lunar backside.

===Calculating phase size===
The phase is equal to the area of the visible lunar sphere that is illuminated by the Sun. This area or ''degree of illumination'' is given by <math>(1-\cos e)/2=\sin^2(e/2)</math>, where <math>e</math> is the [[elongation (astronomy)|elongation]] (i.e., the angle between Moon, the observer on Earth, and the Sun).

== Orientation by latitude ==
[[File:Moon phases by latitude.svg|thumb|right|The observed orientation of the Moon at different phases from different latitudes on Earth (the different orientation displayed between the phases at each latitude show merely the extremes of orientation due to [[libration]])]]

In the [[Northern Hemisphere]], if the left side of the Moon is dark, then the bright part is thickening, and the Moon is described as [[wikt:wax|waxing]] (shifting toward full moon). If the right side of the Moon is dark, then the bright part is thinning, and the Moon is described as waning (past full and shifting toward new moon). Assuming that the viewer is in the Northern Hemisphere, the right side of the Moon is the part that is always waxing. (That is, if the right side is dark, the Moon is becoming darker; if the right side is lit, the Moon is getting brighter.)

In the [[Southern Hemisphere]], the Moon is observed from a perspective inverted, or rotated 180°, to that of the Northern and to all of the images in this article, so that the opposite sides appear to wax or wane.

Closer to the [[Equator]], the [[lunar terminator]] will appear horizontal during the morning and evening. Since the above descriptions of the lunar phases only apply at [[middle latitude|middle]] or [[polar regions of Earth|high latitudes]], observers moving towards the [[tropics]] from northern or southern latitudes will see the Moon rotated anti-clockwise or clockwise with respect to the images in this article.

The lunar crescent can open upward or downward, with the "horns" of the crescent pointing up or down, respectively. When the Sun appears above the Moon in the sky, the crescent opens downward; when the Moon is above the Sun, [[wet moon|the crescent opens upward]]. The crescent Moon is most clearly and brightly visible when the Sun is below the horizon, which implies that the Moon must be above the Sun, and the crescent must open upward. This is therefore the orientation in which the crescent Moon is most often seen from the tropics. The waxing and waning crescents look very similar. The waxing crescent appears in the western sky in the evening, and the waning crescent in the eastern sky in the morning.
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==Other observational phenomena==
===Lunar libration===
[[File:Lunar libration with phase Oct 2007 (continuous loop).gif|thumb|right|240px|Animation showing progression of the Moon's phases.]]

As seen from Earth, the Moon's eccentric orbit makes it both slightly change its apparent size, and to be seen from slightly different angles.

The effect is subtle to the naked eye, from night to night, yet somewhat obvious in time-lapse photography.

Lunar libration causes part of the back side of the Moon to be visible to a terrestrial observer some of the time. Because of this, around 59% of the Moon's surface has been imaged from the ground.
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=== Effect of parallax ===
{{main|Lunar parallax}}
The [[Earth]] subtends an angle of about two degrees when seen from the Moon. This means that an observer on Earth who sees the Moon when it is close to the eastern horizon sees it from an angle that is about 2 degrees different from the line of sight of an observer who sees the Moon on the [[West|western horizon]]. The Moon moves about 12 degrees around its orbit per day, so, if these observers were stationary, they would see the phases of the Moon at times that differ by about one-sixth of a day, or 4 hours. But in reality, the observers are on the surface of the rotating Earth, so someone who sees the Moon on the [[East|eastern horizon]] at one moment sees it on the western horizon about 12 hours later. This adds an oscillation to the apparent progression of the lunar phases. They appear to occur more slowly when the Moon is high in the sky than when it is below the horizon. The Moon appears to move jerkily, and the phases do the same. The amplitude of this oscillation is never more than about four hours, which is a small fraction of a [[month]]. It does not have any obvious effect on the appearance of the Moon. It does however affect accurate calculations of the times of lunar phases.

=== Earthshine ===
[[File:Lumiere cendrée (12273290216).jpg|thumb|right|An [[exposure (photography)|overexposed]] photograph of a crescent Moon reveals earthshine and stars.]]
{{Main|Earthlight (astronomy)}}

When the Moon (seen from Earth) is a thin [[crescent]], Earth (as viewed from the Moon) is almost fully lit by the Sun. Often, the dark side of the Moon is dimly illuminated by indirect sunlight reflected from Earth, but is bright enough to be easily visible from Earth. This phenomenon is called [[earthlight (astronomy)|earthshine]], sometimes picturesquely described as "the old moon in the new moon's arms" or "the new moon in the old moon's arms".
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== Misconceptions ==
=== Orbital period ===
It can be confusing that the Moon's orbital sidereal period is 27.3 days while the phases complete a cycle once every 29.5 days (synodic period). This is due to the Earth's orbit around the Sun. The Moon orbits the Earth 13.4 times a year, but only passes between the Earth and Sun 12.4 times.

=== Eclipses ===
[[File:Eclipse vs new or full moons, annotated.svg|thumb|As the Earth revolves around the Sun, approximate [[axial parallelism]] of the Moon's orbital plane ([[Orbital inclination|tilted]] five degrees to the [[ecliptic|Earth's orbital plane]]) results in the revolution of the [[lunar nodes]] relative to the Earth. This causes an [[eclipse season]] approximately every six months, in which a [[solar eclipse]] can occur at the [[new moon]] phase and a [[lunar eclipse]] can occur at the [[full moon]] phase.]]
[[File:Orbit of the Moon in 2013.ogv|right|thumb|The ''lunar phase'' depends on the Moon's position in orbit around the Earth and the Earth's position in orbit around the Sun. This animation (''not to scale'') looks down on Earth from the north pole of the ecliptic.]]

It might be expected that once every month, when the Moon passes between Earth and the Sun during a new moon, its shadow would fall on Earth causing a [[solar eclipse]], but this does not happen every month. Nor is it true that during every full moon, the [[Earth's shadow]] falls on the Moon, causing a [[lunar eclipse]]. Solar and lunar eclipses are not observed ''every'' month because the plane of the [[Moon's orbit]] around the Earth is tilted by about 5° with respect to the plane of [[Earth's orbit]] around the Sun (the plane of the [[ecliptic]]). Thus, when new and full moons occur, the Moon usually lies to the north or south of a direct line through the Earth and Sun. Although an [[eclipse]] can only occur when the Moon is either new (solar) or full (lunar), it must also be positioned very near the intersection of Earth's orbital plane about the Sun and the Moon's orbital plane about the Earth (that is, at one of [[lunar node|its nodes]]). This happens about twice per year, and so there are between four and seven eclipses in a calendar year. Most of these eclipses are partial; total eclipses of the Moon or Sun are less frequent.

=== Mechanism ===
The phases are not caused by the Earth's shadow falling on the moon, as some people believe.<ref>{{Cite news |last1=Musgrave |first1=Ian |last2=Weule |first2=Genelle |date=January 29, 2018 |title=A beginner's guide to the Moon |url=https://www.abc.net.au/news/science/2018-01-24/beginners-guide-to-the-moon/9320770 |access-date=June 29, 2024 |work=[[Australian Broadcasting Corporation]]}}</ref><ref>{{Cite news |last=Plait |first=Phil |date=December 28, 2012 |title=Today's Full Moon is the 13th and Last of 2012 |url=https://slate.com/technology/2012/12/full-moon-today-is-the-13th-full-moon-of-2012.html |access-date=June 29, 2024 |work=[[Slate (magazine)|Slate]]}}</ref> They are caused by the moon's shadow on itself, just as the Earth's shadow makes it night on one side of the Earth. The angle of the Sun in relation to the Moon determines how much of the Moon is illuminated.

== See also ==
* {{annotated link|Blue moon}}
* {{annotated link|Earth phase}}
* {{annotated link|Lunar effect}}
* {{annotated link|Lunar month}}. (Also known as a "lunation".)
* {{annotated link|Lunar observation}}
* {{annotated link|Planetary phase}}
* {{annotated link|Planetshine#Earthshine|Planetshine}}
* {{annotated link|Tide}}
* {{annotated link|Week}}
* {{annotated link|Month}}
* {{annotated link|Parmenides}}, who tried to explain lunar phases

== Footnotes ==
{{notelist}}

== References ==
===Citations===
{{reflist}}

===Sources===
{{refbegin|2|indent=yes}}
*{{cite web |first1=Leah|last1= Asmelash |first2= David |last2=Allan |title=A black moon is coming on July 31. Here's what that means |url=https://www.cnn.com/2019/07/30/us/black-moon-trnd-scn/index.html |website=CNN|date=30 July 2019 }}
* {{cite book|last1=Buick|first1=Tony |last2=Pugh|first2=Philip |title=How to Photograph the Moon and Planets with Your Digital Camera|url=https://books.google.com/books?id=N4OHwWR9nFMC&pg=PA70|date= 2011|publisher=Springer |isbn=978-1-4419-5828-0}}
* {{cite book|last1=Kelley|first1=David H. |last2=Milone|first2=Eugene F. |title=Exploring Ancient Skies: A Survey of Ancient and Cultural Astronomy|url=https://books.google.com/books?id=ILBuYcGASxcC|year=2011|publisher=Springer |isbn=978-1-4419-7624-6|edition=2nd}}
* {{cite book|last=Kutner|first=Marc L. |title=Astronomy: A Physical Perspective|url=https://archive.org/details/astronomyphysica00kutn|url-access=registration|page=[https://archive.org/details/astronomyphysica00kutn/page/435 435]|year=2003|publisher=Cambridge University Press|isbn=978-0-521-52927-3}}
* {{cite book|last=Lynch|first=Mike |title=Texas Starwatch|date=2007 |url=https://books.google.com/books?id=u3jR5NRgUy0C&pg=PA107+|publisher=Voyageur Press|isbn=978-1-61060-511-3}}
* {{cite book|last=Naylor|first=John |title=Out of the Blue: A 24-Hour Skywatcher's Guide|url=https://books.google.com/books?id=ZQOJGerV2IcC&pg=PA200|year=2002|publisher=Cambridge University Press|isbn=978-0-521-80925-2}}
* {{cite book|last=Ruggles|first=Clive L. N. |title=Ancient Astronomy: An Encyclopedia of Cosmologies and Myth|url=https://books.google.com/books?id=Q9YYqiXm-lkC&pg=PA235|year=2005|publisher=ABC-CLIO|isbn=978-1-85109-477-6}}
*{{cite book|editor-first=P. Kenneth |editor-last=Seidelmann|date=1992|title= Explanatory Supplement to the Astronomical Almanac|publisher=University Science Books|location=Mill Valley|url=https://archive.org/details/131123ExplanatorySupplementAstronomicalAlmanac/page/n1/mode/1up}}
{{refend}}

== External links ==
* [http://astropixels.com/ephemeris/phasescat/phasescat.html Six Millennium Catalog of Phases of the Moon: Moon Phases from -1999 to +4000 (2000 BCE to 4000 CE)].

{{commons category|Lunar phases}}

{{The Moon}}
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[[Category:Phases of the Moon| ]]
[[Category:Observational astronomy]]
[[Category:Technical factors of astrology]]
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