Moon phase

from Wikipedia, the free encyclopedia
Animation of the moon phases. In addition, proximity and distance to the earth can also be observed as fluctuations in size and libration as "staggering".

The changing light shapes of the moon are called moon phases . They arise from the perspective change in the position of its day-night boundary relative to the earth during its orbit. The common division into four quarters, each about a week long. An entire moon phase cycle from one new moon to the following new moon is also called lunation and lasts on average about 29.5 days.

  • A common distinction is made between new moon , waxing moon , full moon and waning moon .
  • The new moon (empty phase) , full moon ( full phase) and the two crescent moons are called the main phases .
  • At half moon , the half phase ( dichotomy ) , half (50%) of the sunlit moon surface is visible. Astronomers refer to the divisions of the full cycle of the moon when they call the waxing half-phase the first quarter and the waning half-phase the last quarter .
  • The waxing moon can be seen during the first quarter of the cycle in the evening sky or in the first half of the night, the waning moon during the last quarter in the second half of the night or in the morning sky .
  • Before the half-phase of the first and after the half-phase of the last quarter, the earth's satellite appears as a crescent moon . When it becomes visible in the evening sky for the first time after the new moon as a very narrow crescent, it is referred to as new light , and when it is last visible in the morning sky before the new moon , it is referred to as old light .


One orbit of the moon around the earth, after which the moon will again assume the same position to the sun , takes an average of about 29.53 days (29 days, 12 hours and 43 minutes). This period of time is called the synodic month and corresponds approximately to the length of a calendar month . In fact, both the term month and the length of the calendar months are derived from the synodic orbit of the moon. The length of a single period - a lunation - is, however, subject to relatively large fluctuations of over ± 6 hours (for the mean, see also synodic period ).

During the movement of the moon around the earth, the angle that is spanned by the connecting lines earth-moon and earth-sun in the imaginary triangle earth-moon-sun changes, the so-called elongation of the moon. For an observer on earth, this changes the perspective with which he sees the moon. This can be seen in the changed position of the day-night boundary on the side facing the earth and thus as a change in the light shape of the moon in the sky above the earth. When going through the moon phase cycle from the new moon, the phase , as the portion of the moon surface that is illuminated by the sun and also visible from the earth, first increases and then decreases again.

The counterpart of elongation is the phase angle of the moon, which is spanned in the imaginary triangle earth-moon-sun by the connecting lines moon-sun and moon-earth. For example, when the crescent moon increases, exactly one half appears illuminated, since the phase angle is exactly 90 °. At this stage, the elongation is almost a right angle at around 89.85 °. The third angle in the imaginary triangle is the one at which the earth-moon distance would appear to an observer on the sun - maximum, at a half moon, about 0.15 °. Because the distance between the sun and the earth and the moon is almost four hundred times greater than the distance between the earth and the moon, from this perspective he would now see both of them at an angular distance of about 9 ' arc minutes , their sun-facing side fully illuminated.

The earth-moon system with a view of the northern hemispheres ...
Moon graphic The moon is illuminated by the sun almost continuously. Since it does not shine itself, only its half illuminated by the sun is always bright. Depending on the position of the moon on its orbit around the earth , an earthly observer sees different amounts of this illuminated half. The apparent lighting phases of the moon that come about in the course of a lunation are called in detail:
  1. New moon (elongation = 0 °; phase angle = 180 °),
  2. first quarter or increasing sickle (eastern elongation <90 °; phase angle> 90 °),
  3. increasing crescent moon (astronomical: first quarter ; eastern elongation ≈ 90 °; phase angle = 90 °),
  4. second quarter (eastern elongation> 90 °; phase angle <90 °),
  5. Full moon (elongation = 180 °; phase angle = 0 °),
  6. third quarter (western elongation> 90 °; phase angle <90 °),
  7. waning crescent (astronomical: last quarter ; western elongation ≈ 90 °; phase angle = 90 °),
  8. last quarter or decreasing sickle (western elongation <90 °; phase angle> 90 °).
... and the moon seen from the northern hemisphere of the earth
Moon phases.svg The moon appears to an observer on earth in the course of a lunation. The usual counting in astronomy starts with the new moon (1). The crescent shape of the moon in the first (2) and last quarter (8) results from the fact that the moon is approximately spherical and therefore the day-night boundary appears more curved the closer it is to the edge of the outline of the earth-facing Side of the moon is coming. The orientation of the crescent moon in the illustration applies to the higher latitudes of the northern hemisphere of the earth. In the southern hemisphere the situation is reversed, while the crescent moon appears lying or hanging near the equator.

A complete cycle from new moon to new moon only comes about during a synodic month. During a simple full earth orbit ( sidereal month , average duration 27.32 days) the moon does not reach the same position to the sun as at the beginning of the orbit because of the movement of the earth on its solar orbit.

Moon legende.svg

A: Earth
B: Earth's moon
C: Orbit of the moon
D: Orbit around the earth
E: Sun rays
Note: The proportions of the objects on the graphics and their distances to one another do not correspond to natural proportions.


The moon is a passive light source; it scatters the light from the active light source, the sun.

  • The part of the moon's surface that is illuminated by the sun appears bright.
  • Parts of the surface on the earth-facing side of the moon that are not illuminated by the sun can still be visible. Because the day side of the earth reflects sunlight as earth light into space, which also reaches the moon; from there it is partially reflected back as so-called ash - gray moonlight . Therefore, for an observer on earth, not only the crescent-shaped light of the moon phase can often be seen, but next to it, much weaker, also the rest of the earth-facing surface. This is still visible even during lunar eclipses , as the sunlight passing through the earth's atmosphere is refracted . Long-wave parts in particular therefore reach the full moon even in the earth's shadow, so that, when darkened, it now appears copper-colored.
  • The times for the moon rise and set vary with the phases and (less) with the season. Details are complicated because of the inclination of the lunar orbit plane to that of the earth as well as the inclined axis of the earth. In addition, the deviations between the actual solar time and the time zone in which the observer is located must be taken into account, especially during the validity of summer time :
  • At a new moon, the moon rises roughly together with the sun in the morning and sets in the evening. After that, the rising and setting take place from day to day on average about 50 minutes later.
  • In the first quarter, the moon rises around noon and sets around midnight.
  • With a full moon, it rises at dusk and sets at dawn and is visible all night (approx. 8 hours in summer, up to 16 hours in winter).
  • In the last quarter it rises around midnight and sets around noon.


The phases of the moon were also called calf in the past . For Martin Luther the waning moon is called old light , the waxing young light .

Light effect of the moon

Waxing moon with 23 percent visible surface, taken about 4 days 16 hours after new moon on October 13, 2018 in the night sky in Berlin. A quarter of an hour before sunset, the crescent moon is only a few degrees above the horizon, which is why it appears reddish, similar to the low-lying sun (see →  Rayleigh scattering ).

As the moon phases change, the night on earth is brightened very differently, and astronomers usually have to avoid the bright “moon nights” around the full moon when observing with optical telescopes .

At the new moon, the earth-facing side of the moon is not illuminated by the sun, so it is dark and - covered by the atmospheric blue of the sky - rises and sets with the sun near it. The new moon is only visible when a solar eclipse occurs, every few years in the same location .

The very narrow new light crescent is so close to the sun that it can only be seen shortly after sunset. A few days after the new moon, the waxing crescent moon is so high in the evening that it can be observed over the horizon in the night sky even after the end of astronomical twilight . One week after the new moon, the crescent moon can be seen for the entire afternoon and shines half the night until it sets around midnight.

Four effects contribute to the strong light effect around the time of the full moon:

  • An observer on earth now sees a surface of the moon that is completely illuminated by the sun shining, i.e. the maximum light shape of the lunar disc during a phase cycle. The solid angle of the full moon disk on the celestial sphere depends on the respective lunar distance. In perigee standing the moon appears bigger and seems brighter than in apogee.
  • The reflection ( albedo ) of the moon is now strongest; from an earthly perspective, the shadows cast on the unevenness of the moon's surface are hidden from view because the angle of incidence of the incident sunlight almost corresponds to the viewing angle. In contrast, the half moon shines with only about 1/9 of the full moon brightness.
  • The moon now reaches its highest point ( culmination ) at midnight, in the otherwise darkest part of the night. When the moon is higher, the moonlight hits the earth's surface at a steeper angle, the luminous flux density is therefore greater and the atmospheric scattering of the light is less.
  • The full moon is visible all night long and separates with the sun when it rises and sets.

When the sky is clear, a high full moon, which is more common in winter , illuminates the earth for a few hours so brightly even at sea level that colors can be perceived with the dark-adapted human eye, for example a meadow appears green. The illuminance is then up to 0.25  lux , 250 times that of a starry new moon night (0.001 lux).

The more you stay, move or live without artificial light sources (city, electricity, vehicle and street lighting, hidden by mountains, vegetation, without fire), the stronger you become as a sighted person with moonlight - depending on the moon phases and cloud cover influences its possibilities at night. On a lonely road with no shadows from trees, when the moon is full you have a view that is actually sufficient for running and (lonely) cycling and evenly bright to the horizon. Street lighting and bicycle lights are at least 40 times as bright at around 10 lx or more, but only in the illuminated area. Such lighting also largely fades the illumination of the distance by moonlight.


In numerous books, a connection between moon phases and different life situations is established. The position of the moon is said to have an impact on sleep , the frequency of accidents, complications during operations and births, and hair growth . Studies have not been able to find any evidence for any such claim and are therefore considered to be refuted .

In particular, the alleged moon phase cycle of 28 days (actually a good 29.5 days) has influenced the concept of " biorhythms " that are supposed to affect all areas of life in German-speaking countries for over a hundred years . There is also a persistent conviction that the alleged average length of the menstrual cycle of human women of 28 days can be explained by the allegedly 28-day moon phase cycle . It has long been known in gynecology that the cycle can fluctuate between 23 and 35 days even in healthy women. This theory is also unable to explain why the menstrual cycles in the various mammals are of different lengths and why their duration differs greatly on average from the moon phase cycle.

Moon phase and tidal range

Origin of tidal forces by the moon: tidal forces on the earth's surface as the sum of the gravitational force of the moon and the
centrifugal force caused by the revolution of the earth around the center of the bary . The reference system is the earth.

Very often the tides are mistakenly attributed to the gravity of the moon alone. The 3-phase changeable sea level is rather explained by the interaction of (a.) The gravitation of the moon plus (b.) The centrifugal force of the common earth-moon center of mass barycenter and (c.) The gravitation of the sun.

Gravity of the moon

The tides are triggered by the gravitation of the nearby moon, which, due to its own motion, apparently orbits the earth in 29.53 days less often than the sun does. During an apparent lunar orbit of 24h 49min, water is pulled together to form a tidal wave when the moon is at its highest level (the actual tidal wave, however, runs as a flow process around the earth's equator with a time delay, accumulates on coasts, sloshes up in constrictions and resonates in places).

Centrifugal force due to the movement around the earth-moon center of mass

Earth and moon revolve around their common center of gravity - illustration not true to scale

As a system of two celestial bodies rotating together, earth and moon have a common center of mass ( barycenter ). This lies on the line connecting the centers of the earth and moon, but due to the much larger mass of the earth, it is inside the earth's body. On the side facing away from the moon, the forces of gravity are counteracted by higher centrifugal forces. The liquid and gaseous elements are therefore "thrown off". The 2-phase (24h 49min) / 2 is explained by the interaction of the gravitation of the moon and the barycentre.

Gravity of the sun

The sun supports the effect of the moon to the maximum when the three celestial bodies involved are on one line, i.e. with full and new moon: Spring tide occurs every 14.77 days, i.e. the highest tidal range between ebb and flow . On the other hand, nipp tide when the moon, earth and sun are at right angles to each other in an L-configuration, i.e. at a half moon.

For example, the phases of the moon - theoretically around the phase delay of the tidal wave, i.e. a little ahead - show the exact sequence of high and low tidal range as an indicator, which, however, is still practically overlaid by the effects of wind and weather (air pressure).

Donkey bridges

An older German rule of thumb for the light figure of the moon phases is based on the German cursive : When writing the letter a , you start with an arch curved to the left. This shows the orientation of the narrow crescent of a bnehmenden moon, as seen by an observer in the northern hemisphere. The example of the handwriting on the other hand with an arched right arc begun and represents the z unehmenden moon.

A Latin Wish rule is luna mentitur (translated: "The moon is lying") with similar terms of letter forms: the crescent moon shows us when removing a C as crescens (increasingly), and it shows us the rise a D as decrescens (, decreasing ').

"Lying" sickle of the waxing moon, as it can be observed near the earth's equator (here from the southern tip of India, at 9.5 ° north latitude )

A more modern shopping rule uses the characters " ( ", as "clamp a uf" for " a bnehmend" and " ) ", "clip on " for " to taking", the shape of which in each case represents the crescent moon. The two mathematical symbols " < " ( " smaller than"; for " from taking") and " > " ( " greater than"; for " to taking") are suitable for this.

All these rules of thumb apply in this form only in middle to high northern latitudes; In the southern middle to high latitudes, however, the reverse is true. Due to the almost horizontal position of a crescent moon when rising and setting, they are difficult to use between the tropics and depending on the season.


There are symbols for the phases of the moon in both astronomy and astrology . These represent the phase as a pictogram. Sometimes they are also decorated with faces . Since they are of European origin, they correspond to the sight of the moon in the northern hemisphere. In the southern hemisphere, the moon is seen upside down, which can confuse the symbols.

symbol meaning
without with face
new moon New moon with face New moon with face new moon
Waxing crescent moon Waxing crescent moon with face Waxing crescent moon with face Waxing crescent moon ( new light in the first days after new moon); Planetary metal silver , Monday ; Lunar or solar eclipse
Increasing crescent Waxing Crescent, First Quarter
Increasing Moon Waxing moon (no specific name)
Full moon Full moon with face Full moon with face Full moon , second quarter
Waning moon Waning moon (no specific name)
Waning crescent Waning crescent, last quarter
Waning crescent moon Waning crescent moon with face Waning crescent moon with face Waning crescent moon ( old light in the last days before new moon); Moon as celestial body; Lunar or solar eclipse

Possible confusion

The commonly known phases of the moon are to be distinguished from the terms nosing and obsessive . These terms, which come from Upper German , are mostly translated as the rising and falling moon . What is meant is that the orbit of the moon across the sky seems to run higher and higher from day to day during one half of the month, whereas the opposite is the case during the other half of the month ( tropical month ).

See: Topocentric lunar orbit


The second full moon in a month and the third full moon in a season with four full moons is known as the blue moon . In the case of the new moon, this is known as the "Black Moon".

A full moon during a total umbra eclipse is also known as a "blood moon" because of its color.

At a moon age of around 6.7 days, i.e. shortly before reaching the first quarter of the moon , the visual effects Lunar X and Lunar V can be observed on the moon terminator . At a moon age of around 10.5 days, the golden handle can also be observed on the terminator .

The phases of the moon are independent of the current distance between the moon and the earth on its elliptical orbit ( anomalous month ). If the moon is closest to the earth ( perigee ) during the full moon , this is known as the " super moon ".


  • Alexander Angermann: Does the moon have an influence on the surgeon? An examination based on hip replacement surgery . From the Orthopedic Clinic and Polyclinic of the Ludwig Maximilians University in Munich; Director: Volkmar Jansson, Munich 2011, DNB 1014972477 (Dissertation on the acquisition of a doctorate in medicine at the Medical Faculty of the Ludwig Maximilians University in Munich 2011, 58 pages full text online PDF, free of charge, 61 pages, 1 MB).

Web links

Commons : phases of the moon  - collection of images, videos and audio files
Wiktionary: Moon phase  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. At the apex of this angle is the earth, see entry Elongation in the spectrum online lexicon of physics, accessed on December 7, 2018.
  2. Eckart Kuphal: Rediscover the moon . Springer, 2003, ISBN 978-3-642-37724-2 , pp. 8 ( ).
  3. see on this: Jörg Mildenberger: Anton Trutmanns "Pharmacopoeia". Part 2: Dictionary. Volume 5: W - Z (= Würzburg medical-historical research. Volume 56, ISSN  0344-6948 ). Königshausen & Neumann, Würzburg 1997, p. 2229.
  4. Martin Luther: All works. Department 3: Exegetical German writings. Volume 10. After the oldest editions, edited critically and historically by Johann Konrad Irmischer. Heyder, Erlangen 1847, p. 206.
  5. Animation of the lunations of 2018 , APOD (NASA) from September 12, 2018.
  6. Otto Struve, Beverly T. Lynds, Helen Pillans: Astronomy: Introduction to its Basics . Walter de Gruyter, 1967, ISBN 978-3-11-154310-9 , p. 119 f . ( ).
  7. Moon phases - studies refute alleged moon influences . Retrieved April 12, 2011.
  8. Sebastian Herrmann: Triumphant advance of the lunar calendar on . Retrieved April 12, 2011.
  9. Mark Benecke: Twenty-three . In: The Skeptic . No. 2 , 2010, p. 92–96 ( archived from the original on 2011-11-08 ( memento of November 8, 2011 in the Internet Archive )). Twenty-three ( memento of the original from November 8, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot /
  10. ^ Elisabeth Raith-Paula, Petra Frank-Hermann, Günter Freundl, Thomas Strowitzki: Natural family planning today. (Modern cycle knowledge for advice and application). 4th, revised and expanded edition. Springer, Heidelberg 2008, ISBN 978-3-540-73439-0 , p. 131.
  11. Lunar headstand . Retrieved February 16, 2016.