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Information about Lunar Phase

“Moon phase” redirects here. For the fictional series, see Tsukuyomi -Moon Phase-.


Lunar phase refers to the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases vary cyclically as the Moon orbits the Earth, according to the changing geometry of the Earth, Moon, and Sun. One half of the lunar surface is always illuminated by the Sun (except during lunar eclipses), and is hence bright, but the portion of the illuminated hemisphere that is visible to an observer can vary from 100% (full moon) to 0% (new moon). The boundary between the illuminated and unilluminated hemispheres is called the terminator.

Overview

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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 diagram looks down on Earth from the north. Earth's rotation and the Moon's orbit are both counter-clockwise here. Sunlight is coming in from the right, as indicated by the yellow arrows. From this diagram, we can see, for example, that the full moon will always rise at sunset, and that the waning crescent moon is high overhead around 9:00 AM local time.
Lunar phases are the result of our eyes seeing the illuminated half of the Moon from different viewing geometries: they are not caused by shadows of the Earth on the Moon that occur during a lunar eclipse. The Moon exhibits different phases as the relative geometry of the Sun, Earth, and Moon change, appearing as a full moon when the Sun and Moon are on opposite sides of the Earth, and as a new moon (also named dark moon) it is not visible at night when they are on the same side. The phases of full moon and new moon are examples of syzygies, which occur when the Earth, Moon, and Sun lie (approximately) in a straight line. The time between two full moons (or between successive occurrences of the same phase) is about 29.53 days (29 days, 12 hours, 44 minutes) on average. This synodic month is longer than the time it takes the Moon to make one orbit about the Earth with respect to the fixed stars (the sidereal month), which is about 27.32 days. This difference is caused by the fact that the Earth-Moon system is orbiting about the Sun at the same time the Moon is orbiting about the Earth. The actual time between two syzygies is variable because the orbit of the Moon is elliptic and subject to various periodic perturbations, which change the velocity of the Moon.

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. Likewise, during every full moon, we might expect the Earth's shadow to fall on the Moon, causing a lunar eclipse. We do not observe a solar and lunar eclipse every month because the plane of the Moon's orbit around the Earth is tilted by about 5 degrees with respect to the plane of Earth's orbit around the Sun. 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 or full, it must also be positioned at (or very nearly at) the intersection of Earth's orbit plane about the Sun and the Moon's orbit plane about the Earth (that is, at one of its nodes). This happens about twice per year, and so there are between 4 and 7 eclipses in a calendar year. Most of these are quite insignificant; major eclipses of the Moon or Sun are rather rare.

Names of lunar phases

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Phases of the Moon, as seen from the Northern Hemisphere.
The phases of the Moon have been given the following names, which are listed in sequential order:
Phase Northern Hemisphere Southern Hemisphere
Dark MoonNot visibleNot visible
New MoonNot visible, or traditionally, the first visible crescent of the Moon
Waxing Crescent MoonRight 1-49% visibleLeft 1-49% visible
First Quarter MoonRight 50% visibleLeft 50% visible
Waxing gibbous MoonRight 51-99% visibleLeft 51-99% visible
Full MoonFully visibleFully visible
Waning gibbous MoonLeft 51-99% visibleRight 51-99% visible
Third Quarter MoonLeft 50% visibleRight 50% visible
Waning Crescent MoonLeft 1-49% visibleRight 1-49% visible
When the Sun and Moon are aligned on the same side of the Earth, the Moon is "new", and is not illuminated by the Sun. As the Moon waxes (the amount of illuminated surface as seen from Earth is increasing), the lunar phases progress from new moon, crescent moon, first-quarter moon, gibbous moon and full moon phases, before returning through the gibbous moon, third-quarter moon, crescent moon and new moon phases. The terms old moon and new moon are interchangeable, although new moon is more common. Half moon is often used to mean the first- and third-quarter moons.

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Animation of the Moon as it cycles through its phases, as seen from the Northern Hemisphere. The apparent wobbling of the Moon is known as libration.
When a sphere is illuminated on one hemisphere and viewed from a different angle, the portion of the illuminated area that is visible will have a two-dimensional shape defined by the intersection of an ellipse and circle (where the major axis of the ellipse coincides with a diameter of the circle). If the half-ellipse is convex with respect to the half-circle, then the shape will be gibbous (bulging outwards), whereas if the half-ellipse is concave with respect to the half-circle, then the shape will be a crescent.

In the northern hemisphere, if the left side of the Moon is dark then the light part is growing, and the Moon is referred to as waxing (moving towards a full moon). If the right side of the Moon is dark then the light part is shrinking, and the Moon is referred to as waning (moving towards a new moon). Assuming that one is in the northern hemisphere, the right portion of the Moon is the part that is always growing. The acronym mnemonic "DOC" represents this: "D" is the waxing moon; "O" the full moon; and "C" the waning moon. (One phrase that can be used to remember this is "Dog comes; Cat goes".) In the Southern hemisphere, this order is reversed, and the mnemonic is "COD".

Calendar

Main article: Lunar calendar
The average calendrical month, which is 1/12 of a year, is about 30.4 days, while the Moon's phase (synodic) cycle repeats every 29.53 days. Therefore the timing of the Moon's phases shifts by an average of about one day for each successive month. If you photographed the Moon's phase every day for a month, starting in the evening after sunset, and repeating approximately 25 minutes later each successive day, ending in the morning before sunrise, you could create a composite image like the example calendar below from May 8, 2005 to June 6, 2005. Note that there is no picture on May 20 since a picture would be taken before midnight on May 19, and after midnight on May 21. For a similar reason, if you look at a calendar listing moon rise or set times, there will be days where the moon never rises or sets.

See also

External links

 •  • [ e]
The Moon
GeneralCalendar Month Moon in art and literature Moon in mythology Moon illusion Lunar effect
OrbitOrbit of the Moon Phases of the Moon Solar eclipse Lunar eclipse Tides
Physical characteristicsInternal structure Gravity field Topography Magnetic field Atmosphere
The lunar surfaceSelenography Near side Far side Lunar mare Impact crater South Pole-Aitken basin Shackleton (crater) Ice Peak of eternal light Space weathering Transient lunar phenomenon
Lunar scienceGeology Lunar geologic timescale Giant impact hypothesis Moon rocks Lunar meteorites KREEP ALSEP Lunar laser ranging Late heavy bombardment
ExplorationExploration of the Moon Project Apollo Robotic exploration Future missions Lunar colonization Moon Landing hoax accusations
See also Solar system, natural satellite

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Moon  

The Moon as seen by an observer on Earth
Orbital characteristics
Periapsis: 363,104 km
0.0024 AU
Apoapsis: 405,696 km
0.0027 AU
Semi-major axis: 384,399 km
0.
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ORBit is a CORBA compliant Object Request Broker (ORB). The current version is called ORBit2 and is compliant with CORBA version 2.4. It is developed under the GPL license and is used as middleware for the GNOME project.
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The Sun

Observation data
Mean distance
from Earth 1.4961011 m
(8.31 min at light speed)
Visual brightness (V) −26.74m [1]
Absolute magnitude 4.
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The Sun

Observation data
Mean distance
from Earth 1.4961011 m
(8.31 min at light speed)
Visual brightness (V) −26.74m [1]
Absolute magnitude 4.
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lunar eclipse occurs whenever the Moon passes through some portion of the Earth's shadow. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, the Moon is always full near a lunar eclipse.
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Full Moon may refer to:
  • Full moon, the phase of the moon
  • Full Moon (band), a late '70s/early '80s hard rock band
  • Full Moon (album), a 2002 album by Brandy Norwood which also includes a song of the same name:

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New Moon is the lunar phase that occurs when the Moon, in its monthly orbital motion around Earth, lies between Earth and the Sun, and is therefore in conjunction with the Sun as seen from Earth.
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terminator is the line between the illuminated, day side and dark, night side of a planetary body (also known as the "grey line" or the "twilight zone"). It is defined as the locus of points on a moon or planet where the line through the sun is tangent.
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lunar eclipse occurs whenever the Moon passes through some portion of the Earth's shadow. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, the Moon is always full near a lunar eclipse.
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Full Moon may refer to:
  • Full moon, the phase of the moon
  • Full Moon (band), a late '70s/early '80s hard rock band
  • Full Moon (album), a 2002 album by Brandy Norwood which also includes a song of the same name:

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New Moon is the lunar phase that occurs when the Moon, in its monthly orbital motion around Earth, lies between Earth and the Sun, and is therefore in conjunction with the Sun as seen from Earth.
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Dark moon is the period when the Moon appears so close to the Sun in the sky that it cannot be seen even near sunset or sunrise. Depending on how close the Moon passes to the line between Earth and Sun, dark moon may last between 1.5 to 3.5 days.
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Syzygy (IPA: /ˈsɪzɨʤi/) is a kind of unity, especially through coordination or alignment, most commonly used in the astronomical and/or astrological sense.
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The orbital period is the time taken for a planet (or another object) to make one complete orbit.

When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.
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ORBit is a CORBA compliant Object Request Broker (ORB). The current version is called ORBit2 and is compliant with CORBA version 2.4. It is developed under the GPL license and is used as middleware for the GNOME project.
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solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partially obscuring Earth's view of the Sun. This configuration can only occur during a new moon, when the Sun and Moon are in conjunction as seen from the Earth.
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lunar eclipse occurs whenever the Moon passes through some portion of the Earth's shadow. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, the Moon is always full near a lunar eclipse.
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ECLiPSe is a constraint logic programming system that implements a programming language close to Prolog. ECLiPSe was developed until 1995 at the European Computer‐Industry Research Centre (ECRC) in Munich and then until 2005 at the Centre for Planning and Resource Control at
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lunar nodes are the orbital nodes of the Moon, that is, the points where the orbit of the Moon crosses the ecliptic (which is the apparent path of the Sun across the heavens against the background stars).
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ECLiPSe is a constraint logic programming system that implements a programming language close to Prolog. ECLiPSe was developed until 1995 at the European Computer‐Industry Research Centre (ECRC) in Munich and then until 2005 at the Centre for Planning and Resource Control at
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Northern Hemisphere or northern hemisphere[1] is the half of a planet that is north of the equator—the word hemisphere literally means 'half ball'. It is also that half of the celestial sphere north of the celestial equator.
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Southern Hemisphere or southern hemisphere[1] is the half of a planet that is south of the equator—the word hemisphere literally means 'half ball'. It is also that half of the celestial sphere south of the celestial equator.
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crescent is generally the shape produced when a circular disk has a segment of another circle removed from its edge, so that what remains is a shape enclosed by two circular arcs of different diameters which intersect at two points (usually in such a manner that the enclosed shape
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crescent is generally the shape produced when a circular disk has a segment of another circle removed from its edge, so that what remains is a shape enclosed by two circular arcs of different diameters which intersect at two points (usually in such a manner that the enclosed shape
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Northern Hemisphere or northern hemisphere[1] is the half of a planet that is north of the equator—the word hemisphere literally means 'half ball'. It is also that half of the celestial sphere north of the celestial equator.
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Southern Hemisphere or southern hemisphere[1] is the half of a planet that is south of the equator—the word hemisphere literally means 'half ball'. It is also that half of the celestial sphere south of the celestial equator.
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lunar calendar is a calendar in many cultures that is oriented at the moon phase.

This is normally done by having a month which corresponds to a lunation so that the day of month indicates the moon phase. If a calendar tracks the seasons, it is also a lunisolar calendar.
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Full Moon may refer to:
  • Full moon, the phase of the moon
  • Full Moon (band), a late '70s/early '80s hard rock band
  • Full Moon (album), a 2002 album by Brandy Norwood which also includes a song of the same name:

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For the Egyptian hawk-god, see .


The month is a unit of time, used with calendars, which is approximately as extensive as some natural period related to the motion of the Moon.
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