Composite image of theApril 2014 total lunar eclipse as viewed fromCharleston, West VirginiaA schematic diagram of the shadow cast by Earth. Within theumbra, the central region, the planet totally shields directsunlight. In contrast, within thepenumbra, the outer portion, the sunlight is only partially blocked.Sun,Moon, and Earth sizes and distances between them not to scale.
Alunar eclipse, also called ablood moon, is anastronomical event that occurs when theMoon orbits throughEarth's shadow.[1][2] Lunar eclipses occur duringeclipse season, when the Moon'sorbital plane is approximately in line withEarth and theSun. The type and length of a lunar eclipse depend on the Moon's proximity to thelunar node.[3][4] In contrast with illusive and short-lastingsolar eclipses, lunar eclipses can be observed from anywhere on thenight side of Earth and often last for an hour or longer.[5] Lunar eclipses are safe to observe withouteye protection.[6]
Lunar eclipses are notable for causing the Moon to appearorange orred. This occurs when the Moon passes through the Earth'sumbra, necessitating anysunlight that reaches the Moon to first pass through the Earth'satmosphere. The resultingRayleigh scattering removes high-wavelength colors such asviolet andblue from the incoming light before it reflects off the lunar surface and is observed on Earth.[7]
A penumbral lunar eclipse occurs when Earth's silhouette partially blocks the Sun in the lunar sky but does not occlude it completely, ensuring some sunlight can still reach the Moon directly. The designation refers to the Moon being partially inside of thepenumbra, which describes the region of any shadow that is cast by a light source which is notcollimated and has a non-zeroangular diameter. A penumbral eclipse is designated as atotal penumbral eclipse if the moon lies exclusively inside of the penumbra.
Penumbral eclipses are observed from Earth as a subtle dimming of the lunar surface.[8][9] Of all lunar eclipses, approximately one-third are penumbral eclipses; of those, only 3% are total penumbral eclipses.[10]
A partial lunar eclipse refers to the Moon lying partially inside of theumbra, where the relative size of the Earth in the lunar sky allows it to block the Sun entirely. During a partial eclipse, the dark region covered by the umbra will appear more much more distinct than the penumbral dimming.
The Moon's averageorbital speed is about 1.03 km/s (2,300 mph), or a little more than its diameter per hour, so totality may last up to nearly 107minutes. Nevertheless, the total time between the first and last contacts of the Moon's limb with Earth's shadow is much longer and could last up to 236minutes.[11]
Total lunar eclipse
When the Moon's near side entirely passes into the Earth's umbral shadow, a total lunar eclipse occurs.[12] Just prior to complete entry, the brightness of the lunar limb—the curved edge of the Moon still being hit by direct sunlight—will cause the rest of the Moon to appear comparatively dim. The moment the Moon enters a complete eclipse, the entire surface will become more or less uniformly bright, being able to reveal stars surrounding it. Later, as the Moon's opposite limb is struck by sunlight, the overall disk will again become obscured.
This is because, as viewed from the Earth, the brightness of a lunar limb is generally greater than that of the rest of the surface, due to reflections from the many surface irregularities within the limb: sunlight striking these irregularities is always reflected back in greater quantities than that striking more central parts, which is why the edges of full moons generally appear brighter than the rest of the lunar surface. This is similar to the effect ofvelvet fabric over a convex curved surface, which, to an observer, will appear darkest at the center of the curve. It will be true of any planetary body with little or no atmosphere and an irregular cratered surface (e.g., Mercury) when viewed opposite the Sun.[13]
Central lunar eclipse
When, during a total lunar eclipse, the Moon passes near and through the centre of Earth's shadow, contacting theantisolar point, it is classified as a central lunar eclipse.[14] This type of lunar eclipse isless frequent, occurring in 59.6% of all total lunar eclipses.[10]
Therelative distance of the Moon from Earth at the time of an eclipse can affect the eclipse's duration. In particular, when the Moon is nearapogee, the farthest point from Earth inits orbit, itsorbital speed is the slowest. The diameter of Earth's umbra does not decrease appreciably within the changes in the Moon's orbital distance. Thus, the concurrence of a totally eclipsed Moon near apogee will lengthen the duration of totality.[15]
Aselenelion orselenehelion, also called ahorizontal eclipse, occurs where and when both the Sun and an eclipsed Moon can be observed at the same time. The event can only be observed just beforesunset or just aftersunrise, when both bodies will appear just above oppositehorizons at nearlyopposite points in the sky. A selenelion occurs during every total lunar eclipse—it is an experience of theobserver, not a planetaryevent separate from the lunar eclipse itself. Typically, observers on Earth located on high mountain ridges undergoingfalse sunrise orfalse sunsetat the same moment of a total lunar eclipse will be able to experience it. Although during selenelion the Moon is completely within the Earth's umbra, both it and the Sun can be observed in the sky becauseatmospheric refraction causes each body toappear higher (i.e., more central) in the sky than its true geometric planetary position.[17]
Timing
Contact points relative to the Earth's umbral and penumbral shadows, here with the Moon near its descending node
The timing of total lunar eclipses is determined by what are known as its "contacts" (moments of contact with Earth's shadow):[18]
P1 (First contact): Beginning of the penumbral eclipse. Earth's penumbra touches the Moon's outer limb.
U1 (Second contact): Beginning of the partial eclipse. Earth's umbra touches the Moon's outer limb.
U2 (Third contact): Beginning of the total eclipse. The Moon's surface is entirely within Earth's umbra.
Greatest eclipse: The peak stage of the total eclipse. The Moon is at its closest to the center of Earth's umbra.
U3 (Fourth contact): End of the total eclipse. The Moon's outer limb exits Earth's umbra.
U4 (Fifth contact): End of the partial eclipse. Earth's umbra leaves the Moon's surface.
P4 (Sixth contact): End of the penumbral eclipse. Earth's penumbra no longer makes contact with the Moon.
In a lunar eclipse, the Moon often passes through two regions ofEarth's shadow: an outer penumbra, where direct sunlight is dimmed, and an inner umbra, where indirect and much dimmer sunlightrefracted by Earth's atmosphere shines on the Moon, leaving a reddish color. This can be seen in different exposures of a partial lunar eclipse, for example here with exposures of 1/80, 2/5, and 2 seconds.
There is often confusion between a solar eclipse and a lunar eclipse. While both involve interactions between the Sun, Earth, and the Moon, they are very different in their interactions.
The Moon does not completely darken as it passes through the umbra because of therefraction ofsunlight byEarth's atmosphere into the shadow cone; if Earth had no atmosphere, the Moon would be completely dark during the eclipse.[20] The reddish coloration arises because sunlight reaching the Moon must pass through a long and dense layer of Earth's atmosphere, where it isscattered. Shorterwavelengths are more likely to be scattered by the air molecules andsmall particles; thus, the longer wavelengths predominate by the time the light rays have penetrated the atmosphere. Human vision perceives this resulting light asred. This is the same effect that causessunsets andsunrises to turn the sky a reddish color.[21] An alternative way of conceiving this scenario is to realize that, as viewed from the Moon, the Sun would appear to be setting (or rising) behind Earth.
The amount of refracted light depends on the amount ofdust orclouds in the atmosphere; this also controls how much light is scattered. In general, the dustier the atmosphere, the more that other wavelengths of light will be removed (compared to red light), leaving the resulting light a deeper red color. This causes the resulting coppery-red hue of the Moon to vary from one eclipse to the next. Volcanoes are notable for expelling large quantities of dust into the atmosphere, and a large eruption shortly before an eclipse can have a large effect on the resulting color.[22]
The symbol for a lunar eclipse (or any body in the shadow of another) is (U+1F776🝶).
Several cultures havemyths related to lunar eclipses or allude to the lunar eclipse as being a good or badomen. TheEgyptians saw the eclipse as asow swallowing the Moon for a short time; other cultures view the eclipse as the Moon being swallowed by other animals, such as ajaguar inMayan tradition, or a mythical three-legged toad known asChan Chu inChina.[citation needed] Some societies thought it was a demon swallowing the Moon, and that they could chase it away by throwing stones and curses at it.[23]Ancient Greeks understood the Earth was round, citing the Earth's shadow observed during a lunar eclipse as evidence.[24] SomeHindus believe in the importance of bathing in theGanges River following an eclipse because it will help to achievesalvation.[25]
Inca
Similarly to the Mayans, theIncans believed that lunar eclipses occurred when a jaguar ate the Moon, which is why a blood moon looks red. The Incans also believed that once the jaguar finished eating the Moon, it could come down and devour all the animals on Earth, so they would take spears and shout at the Moon to keep it away.[26]
Mesopotamians
Theancient Mesopotamians believed that a lunar eclipse was when the Moon was being attacked by seven demons. This attack was more than just one on the Moon, however, for the Mesopotamians linked what happened in the sky with what happened on the land, and because the king of Mesopotamia represented the land, the seven demons were thought to be also attacking the king. In order to prevent this attack on the king, the Mesopotamians made someone pretend to be the king so they would be attacked instead of the true king. After the lunar eclipse was over, the substitute king was made to disappear (possibly bypoisoning).[26]
Chinese
In some Chinese cultures, people would ring bells to prevent adragon or other wild animals from biting the Moon.[27] In the 19thcentury, during a lunar eclipse, theChinese navy fired its artillery because of this belief.[28] During theZhou dynasty(c. 1046BC – 256BC), according to theBook of Songs, the sight of a red moon engulfed in darkness was believed to foreshadow famine or disease.[29]
Totality during thelunar eclipse of 15 May 2022. Direct sunlight is being blocked by theEarth, and the only light reaching it is sunlightrefracted by Earth's atmosphere, producing a reddish color.
In the 21st century there are 228 lunar eclipses, an average of 2.28 per year, with at least two every year.[30][31]Total lunar eclipses are less common than partial lunar eclipses. Over a 5,000year span from 2000BCE to 3000CE, 36.3% of lunar eclipses are penumbral, 34.9% are partial, and 28.8% are total.[10] If the date and time of an eclipse is known, the occurrence of upcoming eclipses is predictable using aneclipse cycle, like thesaros. During a saros period, lasting 18years and 11days, there will usually be 70eclipses, of which 29 are lunar.[32] Eclipses occur only during aneclipse season, when the Sun appears to pass near eithernode of theMoon's orbit.
A painting byLucien Rudaux showing how a solar eclipse might appear when viewed from the lunar surface. The Moon's surface appears red because the only sunlight available is refracted through Earth's atmosphere on the edges of Earth, as shown in the sky in this painting.
A lunar eclipse is, on the Moon, asolar eclipse. The occurrence makes Earth's atmosphere appear as a red ring around the dark Earth. One such event was captured by theSurveyor3 camera in1967.[33] A second event was photographed in color by theBlue Ghost Mission1 in2025.[34] During a full moon, the phase during which lunar eclipses take place, the dark side of the Earth is illuminated by the Moon and itsmoonlight.
^Espenak, Fred; Meeus, Jean."Visual Appearance of Lunar Eclipses". NASA.The troposphere and stratosphere act together as a ring-shaped lens that refracts heavily reddened sunlight into Earth's umbral shadow.
^Dobrovol'skii, O. V. (1966)."Comets, Meteors, and the Zodiacal Light". In Mikhailov, A. A. (ed.).Physics of the Solar System. A Course in Astrophysics and Stellar Astronomy. Vol. 3. National Aeronautics and Space Administration. p. 307.
^Di Giovanni, G. (February 2018). "Lunar eclipse brightness and the terrestrial atmosphere".Journal of the British Astronomical Association.128 (1):10–17.Bibcode:2018JBAA..128...10D.
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