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A lunar eclipse is an astronomical event that occurs when the Moon moves into the Earth's shadow, causing the Moon to be darkened. Such an alignment occurs during an eclipse season, approximately every six months, during the full moon phase, when the Moon's orbital plane is closest to the plane of the Earth's orbit.

This can occur only when the Sun, Earth, and Moon are exactly or very closely aligned (in syzygy) with Earth between the other two, which can happen only on the night of a full moon when the Moon is near either lunar node. The type and length of a lunar eclipse depend on the Moon's proximity to the lunar node.

When the Moon is totally eclipsed by the Earth (a "deep eclipse"), it takes on a reddish color that is caused by the planet when it completely blocks direct sunlight from reaching the Moon's surface, as the only light that is reflected from the lunar surface is what has been refracted by the Earth's atmosphere. This light appears reddish due to the Rayleigh scattering of blue light, the same reason sunrises and sunsets are more orange than during the day.

Unlike a solar eclipse, which can only be viewed from a relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of Earth. A total lunar eclipse can last up to nearly two hours (while a total solar eclipse lasts only a few minutes at any given place) because the Moon's shadow is smaller. Also unlike solar eclipses, lunar eclipses are safe to view without any eye protection or special precautions.

The symbol for a lunar eclipse (or any body in the shadow of another) is (U+1F776 🝶).

Types of lunar eclipse

Earth's shadow can be divided into two distinctive parts: the umbra and penumbra. Earth totally occludes direct solar radiation within the umbra, the central region of the shadow. However, since the Sun's diameter appears to be about one-quarter of Earth's in the lunar sky, the planet only partially blocks direct sunlight within the penumbra, the outer portion of the shadow.

Penumbral lunar eclipse

A penumbral lunar eclipse occurs when part or all of the Moon's near side passes into the Earth's penumbra. No part of the moon is in the Earth's umbra during this event, meaning that on all or a part of the Moon's surface facing Earth, the sun is partially blocked. The penumbra causes a subtle dimming of the lunar surface, which is only visible to the naked eye when the majority of the Moon's diameter has immersed into Earth's penumbra. A special type of penumbral eclipse is a total penumbral lunar eclipse, during which the entire Moon lies exclusively within Earth's penumbra. Total penumbral eclipses are rare, and when these occur, the portion of the Moon closest to the umbra may appear slightly darker than the rest of the lunar disk.

Partial lunar eclipse

When the Moon's near side penetrates partially into the Earth's umbra, it is known as a partial lunar eclipse, while a total lunar eclipse occurs when the entire Moon enters the Earth's umbra. During this event, one part of the Moon is in the Earth's umbra, while the other part is in the Earth's penumbra. The Moon's average orbital 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 107 minutes. 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 236 minutes.

Total lunar eclipse

When the Moon's near side entirely passes into the Earth's umbral shadow, a total lunar eclipse occurs. 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 of velvet 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.

Central lunar eclipse

Central lunar eclipse is a total lunar eclipse during which the Moon passes near and through the centre of Earth's shadow, contacting the antisolar point. This type of lunar eclipse is relatively rare.

The relative distance of the Moon from Earth at the time of an eclipse can affect the eclipse's duration. In particular, when the Moon is near apogee, the farthest point from Earth in its orbit, its orbital 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.

Selenelion

A selenelion or selenehelion, also called a horizontal 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 before sunset or just after sunrise, when both bodies will appear just above opposite horizons at nearly opposite points in the sky. A selenelion occurs during every total lunar eclipse—it is an experience of the observer, not a planetary event separate from the lunar eclipse itself. Typically, observers on Earth located on high mountain ridges undergoing false sunrise or false sunset at 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 because atmospheric refraction causes each body to appear higher (i.e., more central) in the sky than its true geometric planetary position.

Timing

The timing of total lunar eclipses is determined by what are known as its "contacts" (moments of contact with Earth's shadow):

• 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.

Danjon scale

The following scale (the Danjon scale) was devised by André Danjon for rating the overall darkness of lunar eclipses:

• L = 0: Very dark eclipse. Moon almost invisible, especially at mid-totality.
• L = 1: Dark eclipse, gray or brownish in coloration. Details distinguishable only with difficulty.
• L = 2: Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra is relatively bright.
• L = 3: Brick-red eclipse. Umbral shadow usually has a bright or yellow rim.
• L = 4: Very bright copper-red or orange eclipse. Umbral shadow is bluish and has a very bright rim.

Lunar versus solar eclipse

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 the refraction of sunlight by Earth's atmosphere into the shadow cone; if Earth had no atmosphere, the Moon would be completely dark during the eclipse. The reddish coloration arises because sunlight reaching the Moon must pass through a long and dense layer of Earth's atmosphere, where it is scattered. Shorter wavelengths are more likely to be scattered by the air molecules and small particles; thus, the longer wavelengths predominate by the time the light rays have penetrated the atmosphere. Human vision perceives this resulting light as red. This is the same effect that causes sunsets and sunrises to turn the sky a reddish color. 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 of dust or clouds 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.

In culture

Several cultures have myths related to lunar eclipses or allude to the lunar eclipse as being a good or bad omen. The Egyptians saw the eclipse as a sow swallowing the Moon for a short time; other cultures view the eclipse as the Moon being swallowed by other animals, such as a jaguar in Mayan tradition, or a mythical three-legged toad known as Chan Chu in China. Some societies thought it was a demon swallowing the Moon, and that they could chase it away by throwing stones and curses at it. The Ancient Greeks correctly believed the Earth was round and used the shadow from the lunar eclipse as evidence. Some Hindus believe in the importance of bathing in the Ganges River following an eclipse because it will help to achieve salvation.

Inca

Similarly to the Mayans, the Incans 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.

Mesopotamians

The ancient 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 by poisoning).

Chinese

In some Chinese cultures, people would ring bells to prevent a dragon or other wild animals from biting the Moon. In the 19th century, during a lunar eclipse, the Chinese navy fired its artillery because of this belief. During the Zhou Dynasty (c. 1046–256 BC) in the Book of Songs, the sight of a Red Moon engulfed in darkness was believed to foreshadow famine or disease.

Blood moon

Certain lunar eclipses have been referred to as "blood moons" in popular articles but this is not a scientifically recognized term. This term has been given two separate, but overlapping, meanings.

The meaning usually relates to the reddish color a totally eclipsed Moon takes on to observers on Earth. As sunlight penetrates the atmosphere of Earth, the gaseous layer filters and refracts the rays in such a way that the green to violet wavelengths on the visible spectrum scatter more strongly than the red, thus giving the Moon a reddish cast. This is possible because the rays from the Sun are able to wrap around the Earth and reflect off the Moon.

Occurrence

At least two lunar eclipses and as many as five occur every year, although total lunar eclipses are significantly less common than partial lunar eclipses. If the date and time of an eclipse is known, the occurrences of upcoming eclipses are predictable using an eclipse cycle, like the saros. Eclipses occur only during an eclipse season, when the Sun appears to pass near either node of the Moon's orbit.

View from the Moon

A lunar eclipse is on the Moon a solar eclipse. The occurrence makes Earth's atmosphere appear as a red ring around the dark Earth. During full moon, the phase when lunar eclipses take place, the dark side of the Earth is illuminated by the Moon and its moon light.

See also

• Lists of lunar eclipses and List of 21st-century lunar eclipses
• Lunar occultation
• Moon illusion
• Orbit of the Moon
• Solar eclipse
• Eclipses in history and culture

References

1. McClure, Bruce (27 July 2018). "Century's Longest Lunar Eclipse July 27". EarthSky. Retrieved 1 August 2018.
2. "Eclipses - NASA Science". science.nasa.gov. Retrieved 13 May 2024.
3. "NASA - Periodicity of Lunar Eclipses". eclipse.gsfc.nasa.gov. Retrieved 13 May 2024.
4. Staff (2023). "PHYS 1350 Astronomy Exam 3 (TXST-Olson)". Quizlet. Archived from the original on 9 November 2023. Retrieved 9 November 2023. "What is a deep eclipse? The smaller star is behind the bigger star"
5. Miller, A.M.; et al. (7 November 2023). "ATel #16328 - ASASSN-23ht: A Deep Eclipse Event". The Astronomer's Telegram. Archived from the original on 9 November 2023. Retrieved 9 November 2023.
6. Link 1969, p. 1.
7. ^ Link 1969, p. 2.
8. H. Mucke, J. Meeus (1992). Canon of Lunar Eclipses -2002 to +2526 (3rd ed.). Astronomisches Büro Wien. p. V.
9. Karttunen, Hannu (2007). Fundamental Astronomy. Springer. p. 139. ISBN 9783540341444.
10. "Lunar Limb Magic". Astronomy.com. 27 November 2018.
11. Westfall, John; Sheehan, William (2014). Celestial Shadows: Eclipses, Transits, and Occultations. Springer. p. 50. ISBN 978-1493915354.
12. "Day and Night World Map". www.timeanddate.com. Retrieved 1 November 2023.
13. Kelly Beatty (26 June 2010). "In Search of Selenelion". Sky & Telescope. Archived from the original on 20 December 2011. Retrieved 8 December 2011.
14. Clarke, Kevin. "On the nature of eclipses". Inconstant Moon. Cyclopedia Selenica. Retrieved 19 December 2010.
15. Deans, Paul; MacRobert, Alan M. (16 July 2006). "Observing and Photographing Lunar Eclipses". Sky & Telescope. F+W. Archived from the original on 20 May 2007. Retrieved 7 January 2007.
16. 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.
17. Littmann, Mark; Espenak, Fred; Willcox, Ken (2008). "Chapter 4: Eclipses in Mythology". Totality Eclipses of the Sun (3rd ed.). New York: Oxford University Press. ISBN 978-0-19-953209-4.
18. Pollack, Rebecca. "Ancient Myths Revised with Lunar Eclipse". University of Maryland. Retrieved 2 October 2014.
19. Ani. "Hindus take a dip in the Ganges during Lunar Eclipse". Yahoo News. Retrieved 2 October 2014.
20. ^ Lee, Jane (14 April 2014). "Lunar Eclipse Myths From Around the World". National Geographic. Archived from the original on 17 April 2014. Retrieved 9 October 2014.
21. Quilas, Ma Evelyn. "Interesting Facts and Myths about Lunar Eclipse". LA Times. Retrieved 2 October 2014.
22. "Mythology of the Lunar Eclipse". LifeAsMyth.com.
23. Kaul, Gayatri (15 June 2011). "What Lunar Eclipse Means in Different Parts of the World". India.com. Retrieved 6 October 2014.
24. Sappenfield, Mark (13 April 2014). "Blood Moon to arrive Monday night. What is a Blood Moon?". The Christian Science Monitor. Retrieved 8 February 2018.
25. Nigro, Nicholas (2010). Knack Night Sky: Decoding the Solar System, from Constellations to Black Holes. Globe Pequot. pp. 214–5. ISBN 978-0-7627-6604-8.
26. "All you need to know about the 'blood moon'". theguardian. 28 September 2015.
27. Jeanna, Bryner (13 May 2022). "Why does the moon turn red during a total lunar eclipse?". Space.com. Retrieved 5 January 2023.

Works cited

• Link, F. (1969). "Lunar Eclipses". Eclipse Phenomena in Astronomy. Springer-Verlag Berlin Heidelberg. pp. 1–121. doi:10.1007/978-3-642-86475-9. ISBN 978-3-642-86475-9. LCCN 68-56208. Retrieved 3 January 2023.

Further reading

• Bao-Lin Liu, Canon of Lunar Eclipses 1500 B.C.-A.D. 3000. Willmann-Bell, Richmond VA, 1992
• Jean Meeus and Hermann Mucke Canon of Lunar Eclipses -2002 to +2526 (3rd edition). Astronomisches Büro, Vienna, 1992
• Espenak, F., Fifty Year Canon of Lunar Eclipses: 1986–2035. NASA Reference Publication 1216, 1989
• Espenak, F. Thousand Year Canon of Lunar Eclipses 1501 to 2500, Astropixels Publishing, Portal AZ, 2014

External links

• Lunar Eclipse Essentials: video from NASA
• Animated explanation of the mechanics of a lunar eclipse Archived 3 June 2013 at the Wayback Machine, University of South Wales
• U.S. Navy Lunar Eclipse Computer Archived 13 August 2011 at the Wayback Machine
• NASA Lunar Eclipse Page
• Search among the 12,064 lunar eclipses over five millennium and display interactive maps
• Lunar Eclipses for Beginners
• Tips on photographing the lunar eclipse from New York Institute of Photography Archived 14 July 2011 at the Wayback Machine
• Lunar Eclipse 8 October 2014 - NASA FULL VERSION on YouTube

v t e Moon
Outline
Physical properties	Internal structure Topography Atmosphere Gravity field Hill sphere Magnetic field Sodium tail Moonlight Earthshine
Orbit	Lunar distance Orbital elements Distance Perigee and apogee Libration Nodes Nodal period Precession Syzygy New moon Full moon Eclipses Lunar eclipse Total penumbral lunar eclipse Tetrad Solar eclipse Solar eclipses on the Moon Eclipse cycle Supermoon Tide Tidal force Tidal locking Tidal acceleration Tidal range Lunar station
Surface and features	Selenography Terminator Limb Hemispheres Near side Far side Poles North pole South pole Face Maria List Mountains Peak of eternal light Valleys Volcanic features Domes Calderas Lava tubes Craters List Ray systems Permanently shadowed craters South Pole–Aitken basin Soil swirls Rilles Wrinkle ridges Rocks Lunar basalt 70017 Changesite-(Y) Water Space weathering Micrometeorite Sputtering Quakes Transient lunar phenomenon Selenographic coordinate system
Science	Observation Libration Lunar theory Origin Giant-impact hypothesis Theia Lunar magma ocean Geology Timescale Late Heavy Bombardment Lunar meteorites KREEP Volcanism Experiments Lunar laser ranging ALSEP Lunar sample displays Apollo 11 Apollo 17 Lunar seismology
Exploration	Missions Apollo program Explorers Probes Landing Colonization Moonbase Tourism Lunar resources
Time-telling and navigation	Lunar calendar Lunisolar calendar Month Lunar month Nodal period Fortnight Sennight Lunar station Lunar distance
Phases and names	New Full Names Crescent Super and micro Blood Blue Black Dark Wet Tetrad
Daily phenomena	Moonrise Meridian passage Moonset
Related	Lunar deities Lunar effect Earth phase Moon illusion Pareidolia Man in the Moon Moon rabbit Craters named after people Artificial objects on the Moon Memorials on the Moon Moon in science fiction list Apollo era futuristic exploration Hollow Moon Moon landing conspiracy theories Moon Treaty "Moon is made of green cheese" Natural satellite Double planet Lilith (hypothetical second moon) Splitting of the Moon
Category

v t e Lunar eclipses
Lists of lunar eclipses	Central total eclipses Total penumbral eclipses Historically significant By century
Lunar eclipses by era	Modern era 20th 21st Future 22nd
Lunar eclipses by saros series	100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163
Partial eclipses	1903 Apr 1914 Mar 1916 Jul 1952 Feb 1952 Aug 1954 Jul 1955 Nov 1956 May 1958 May 1959 Mar 1961 Mar 1961 Aug 1963 Jul 1965 Jun 1970 Feb 1970 Aug 1972 Jul 1973 Dec 1974 Jun 1976 May 1977 Apr 1979 Mar 1981 Jul 1983 Jun 1988 Aug 1990 Aug 1991 Dec 1992 Jun 1994 May 1995 Apr 1997 Mar 1999 Jul 2001 Jul 2005 Oct 2006 Sep 2008 Aug 2009 Dec 2010 Jun 2012 Jun 2013 Apr 2017 Aug 2019 Jul 2021 Nov 2023 Oct 2024 Sep → 2026 Aug 2028 Jan 2028 Jul 2030 Jun 2034 Sep 2035 Aug 2037 Jul 2039 Jun 2039 Nov 2041 May 2041 Nov 2046 Jan 2046 Jul 2048 Jun 2052 Oct 2055 Aug 2075 Jun 2099 Apr
Total eclipses	1504 Mar 1910 May 1913 Sep 1920 May 1950 Apr 1950 Sep 1953 Jan 1953 Jul 1954 Jan 1956 Nov 1957 May 1957 Nov 1960 Mar 1960 Sep 1963 Dec 1964 Jun 1964 Dec 1967 Apr 1967 Oct 1968 Apr 1968 Oct 1971 Feb 1971 Aug 1972 Jan 1974 Nov 1975 May 1975 Nov 1978 Mar 1978 Sep 1979 Sep 1982 Jan 1982 Jul 1982 Dec 1985 May 1985 Oct 1986 Apr 1986 Oct 1989 Feb 1989 Aug 1990 Feb 1992 Dec 1993 Jun 1993 Nov 1996 Apr 1996 Sep 1997 Sep 2000 Jan 2000 Jul 2001 Jan 2003 May 2003 Nov 2004 May 2004 Oct 2007 Mar 2007 Aug 2008 Feb 2010 Dec 2011 Jun 2011 Dec 2014 Apr 2014 Oct 2015 Apr 2015 Sep 2018 Jan 2018 Jul 2019 Jan 2021 May 2022 May 2022 Nov → 2025 Mar 2025 Sep 2026 Mar 2028 Dec 2029 Jun 2029 Dec 2032 Apr 2032 Oct 2033 Apr 2033 Oct 2036 Feb 2036 Aug 2037 Jan 2040 May 2040 Nov 2043 Mar 2043 Sep 2044 Mar 2044 Sep 2047 Jan 2047 Jul 2048 Jan 2050 May 2050 Oct 2051 Apr 2051 Oct 2054 Feb 2054 Aug 2055 Feb 2058 Jun 2065 Jul 2069 May 2072 Aug 2076 Jun 2083 Jul 2084 Jan 2087 May 2090 Sep 2094 Jun 2123 Jun 2170 May
Penumbral eclipses	Partial 23 Mar 1940 22 Apr 1940 16 Oct 1940 1951 Feb 21 1951 Mar 23 1951 Aug 17 1951 Sep 15 1955 Jan 08 1955 Jun 05 1958 Apr 04 1958 Oct 27 1959 Sep 17 1962 Feb 19 1962 Jul 17 1962 Aug 15 1965 Dec 08 1966 May 04 1966 Oct 29 1969 Apr 02 1969 Aug 27 1969 Sep 25 1973 Jan 18 1973 Jun 15 1973 Jul 15 1976 Nov 06 1977 Sep 27 1980 Mar 01 1980 Jul 27 1980 Aug 26 1983 Dec 20 1984 May 15 1984 Jun 13 1984 Nov 08 1987 Apr 14 1987 Oct 07 1991 Jan 30 1991 Jun 27 1991 Jul 26 1994 Nov 18 1995 Oct 08 1998 Mar 13 1998 Aug 08 1998 Sep 06 2001 Dec 30 2002 May 26 2002 Jun 24 2002 Nov 20 2005 Apr 24 2009 Feb 09 2009 Jul 07 2009 Aug 06 2012 Nov 28 2013 May 25 2013 Oct 18 2016 Mar 23 2016 Aug 18 2016 Sep 16 2017 Feb 11 2020 Jan 10 2020 Jun 05 2020 Jul 05 2020 Nov 30 2023 May 05 2024 Mar 25 → 2027 Feb 20 2027 Jul 18 2027 Aug 17 2030 Dec 09 2031 May 07 2031 Jun 05 2031 Oct 30 2034 Apr 03 2035 Feb 22 2038 Jan 21 2038 Jun 17 2038 Jul 16 2038 Dec 11 2042 Apr 05 2042 Oct 28 2045 Mar 03 2045 Aug 27 2048 Dec 20 2049 May 17 2049 Jun 15 2049 Nov 09 2052 Apr 14 2053 Mar 04 2060 Nov 08 2107 May 7 Total 1963 Jan 09 1981 Jan 20 1988 Mar 03 1999 Jan 31 2006 Mar 14 → 2053 Aug 29 2070 Apr 25
Related	Danjon scale Eclipse cycle Eclipse season Eclipses in mythology and culture Gamma Solar eclipse
Category → symbol denotes next eclipse in series

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