Lunar eclipse

A lunar eclipse occurs when the Moon passes directly behind Earth and into its shadow.[1] This can occur only when the Sun, Earth, and Moon are exactly or very closely aligned (in syzygy), with Earth between the other two. A lunar eclipse can occur only on the night of a full moon. The type and length of a lunar eclipse depend on the Moon's proximity to either node of its orbit.

During a total lunar eclipse, Earth completely blocks direct sunlight from reaching the Moon. The only light reflected from the lunar surface has been refracted by Earth's atmosphere. This light appears reddish for the same reason that a sunset or sunrise does: the Rayleigh scattering of bluer light. Due to this reddish color, a totally eclipsed Moon is sometimes called a blood moon.

Unlike a solar eclipse, which can be viewed only from a certain relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of Earth. A total lunar eclipse lasts a few hours, whereas a total solar eclipse lasts only a few minutes as viewed from any given place, due to the smaller size of the Moon's shadow. Also unlike solar eclipses, lunar eclipses are safe to view without any eye protection or special precautions, as they are dimmer than the full Moon.

For the date of the next eclipse, see the section Recent and forthcoming lunar eclipses.

Lunar Total Eclipse on July 27, 2018 (100 2006) (43696968392) (cropped)
Totality during the lunar eclipse of 27 July 2018. Direct sunlight is being blocked by the Earth, and the only light reaching it is sunlight refracted by Earth's atmosphere, producing a reddish color.

Types of lunar eclipse

Geometry of a Lunar Eclipse
A schematic diagram of the shadow cast by Earth. Within the umbra, the central region, the planet totally shields direct sunlight. In contrast, within the penumbra, the outer portion, the sunlight is only partially blocked. (Neither the Sun, Moon, and Earth sizes nor the distances between the bodies are to scale.)
Penumbral lunar eclipse 1999 jan 31
A total penumbral lunar eclipse dims the Moon in direct proportion to the area of the Sun's disk covered by Earth. This comparison of the Moon (within the southern part of Earth's shadow) during the penumbral lunar eclipse of January 1999 (left) and the Moon outside the shadow (right) shows this slight darkening.

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 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.

A penumbral lunar eclipse occurs when the Moon passes through Earth's penumbra. The penumbra causes a subtle dimming of the lunar surface. A special type of penumbral eclipse is a total penumbral lunar eclipse, during which the 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.

A partial lunar eclipse occurs when only a portion of the Moon enters Earth's umbra, while a total lunar eclipse occurs when the entire Moon enters the planet's umbra. The Moon's average orbital speed is about 2,300 mph (1.03 km/s), 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 the last contacts of the Moon's limb with Earth's shadow is much longer and could last up to four hours.[2]

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.

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


Lunar eclipse at sunrise Minneapolis October 2014
A view of the October 2014 lunar eclipse from Minneapolis, with the setting and partially eclipsed Moon appearing squashed just above the horizon just after sunrise (seen as sunlight shining on the tree in the right image)

A selenelion or selenehelion occurs when both the Sun and an eclipsed Moon can be observed at the same time. This can occur only just before sunset or just after sunrise, when both bodies will appear just above the horizon at nearly opposite points in the sky. This arrangement has led to the phenomenon being also called a horizontal eclipse.

Typically, a number of high ridges undergoing sunrise or sunset can view it. Although the Moon is in Earth's umbra, both the Sun and an eclipsed Moon can be simultaneously seen because atmospheric refraction causes each body to appear higher in the sky than their true geometric positions.[3]


As viewed from Earth, the Earth’s shadow can be imagined as two concentric circles. As the diagram illustrates, the type of lunar eclipse is defined by the path taken by the Moon as it passes through Earth’s shadow. If the Moon passes through the outer circle but does not reach the inner circle, it is a penumbral eclipse; if only a portion of the moon passes through the inner circle, it is a partial eclipse; and if entire Moon passes through the inner circle at some point, it is a total eclipse.
Lunar eclipse contact diagram
Contact points relative to the Earth's umbral and penumbral shadows, here with the Moon near is descending node

The timing of total lunar eclipses are determined by its contacts:[4]

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:[5]

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

Solar lunar eclipse diagram
A solar eclipse occurs in the daytime at new moon, when the Moon is between Earth and the Sun, while a lunar eclipse occurs at night at full moon, when Earth passes between the Sun and the Moon.
Blood Moon Corrected Labels
The Moon does not completely darken as it passes through the umbra because Earth's atmosphere refracts sunlight into the shadow cone.

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.

Lunar eclipse appearance

Lunar eclipse oct 8 2014 Minneapolis 4 46am
In a lunar eclipse, the Moon often passes through two regions of Earth's shadow: an outer penumbra, where direct sunlight is dimmed, and an inner umbra, where indirect and much dimmer sunlight refracted 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.

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.[6] 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.

Lunar eclipse from moon simulation-sep 28 2015
From the Moon, a lunar eclipse would show a ring of reddish-orange light surrounding a silhouetted Earth in the lunar sky.

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.

Eclipse Christophe Colomb
Christopher Columbus predicted a lunar eclipse.

Lunar eclipse 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 three legged toad 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.[7] The Greeks were ahead of their time when they said the Earth was round and used the shadow from the lunar eclipse as evidence.[8] Some Hindus believe in the importance of bathing in the Ganges River following an eclipse because it will help to achieve salvation.[9]


Similarly to the Mayans, the Incans believed that lunar eclipses occurred when a jaguar would eat 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.[10]


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).[10]


In some Chinese cultures, people would ring bells to prevent a dragon or other wild animals from biting the Moon.[11] In the nineteenth century, during a lunar eclipse, the Chinese navy fired its artillery because of this belief.[12] During the Zhou Dynasty in the Book of Songs, the sight of a red Moon engulfed in darkness was believed to foreshadow famine or disease.[13]

Blood moon

Certain lunar eclipses have been referred to as "blood moons" in popular articles but this is not a scientifically-recognized term.[14] This term has been given two separate, but overlapping, meanings.

The first, and simpler, meaning relates to the reddish color a totally eclipsed Moon takes on to observers on Earth.[15] 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.[16]

The second meaning of "blood moon" has been derived from this apparent coloration by two fundamentalist Christian pastors, Mark Blitz and John Hagee.[14][17] They claimed that the 2014–15 "lunar tetrad" of four lunar eclipses coinciding with the feasts of Passover and Tabernacles matched the "moon turning to blood" described in the Book of Joel of the Hebrew Bible.[17] This tetrad was claimed to herald the Second Coming of Christ and the Rapture as described in the Book of Revelation on the date of the first of the eclipses in this sequence on April 15, 2014.[18]


Lunar Eclipse at ESO 2017
This multi-exposure sequence shows the August 2017 lunar eclipse visible from the ESO headquarters.[19]
Blood Moon
This collage shows the transitional stages of a lunar eclipse.

At least two lunar eclipses and as many as five occur every year, although total lunar eclipses are significantly less common. If the date and time of an eclipse is known, the occurrences of upcoming eclipses are predictable using an eclipse cycle, like the saros.

Recent and forthcoming lunar eclipses

Eclipses occur only during an eclipse season, when the Sun appears to pass near either node of the Moon's orbit.

Lunar eclipse series sets from 1998–2002
Descending node   Ascending node
Saros Date
Saros Date
109 1998 Aug 08
Lunar eclipse from moon-1998Aug08
Lunar eclipse chart close-1998Aug08
114 1999 Jan 31
Lunar eclipse from moon-1999Jan31
Lunar eclipse chart close-1999Jan31
119 1999 Jul 28
Lunar eclipse from moon-1999Jul28
Lunar eclipse chart close-1999Jul28
Eclipse Lunar Total 21.01.2000
2000 Jan 21
Lunar eclipse from moon-2000Jan21
Lunar eclipse chart close-2000Jan21
129 2000 Jul 16
Lunar eclipse from moon-2000Jul16
Lunar eclipse chart close-2000jul16
2001 Jan 09
Lunar eclipse from moon-2001Jan09
Lunar eclipse chart close-2001Jan09
2001 Jul 05
Lunar eclipse from moon-2001Jul05
Lunar eclipse chart close-2001Jul05
144 2001 Dec 30
Lunar eclipse from moon-2001Dec30
Lunar eclipse chart close-2001Dec30
149 2002 Jun 24
Lunar eclipse from moon-2002Jun24
Lunar eclipse chart close-2002Jun24
Last set 1998 Sep 06 Last set 1998 Mar 13
Next set 2002 May 26 Next set 2002 Nov 20
Lunar eclipse series sets from 2002–2005
Descending node   Ascending node
111 2002 May 26
Lunar eclipse from moon-2002May26
Lunar eclipse chart close-2002May26
116 2002 Nov 20
Lunar eclipse from moon-2002Nov20
Lunar eclipse chart close-2002Nov20
Lunar eclipse May 2003-TLR75
2003 May 16
Lunar eclipse from moon-2003May16
Lunar eclipse chart close-03may16
Lunar eclipse November 2003-TLR63
2003 Nov 09
Lunar eclipse from moon-2003Nov09
Lunar eclipse chart close-03nov09
Total lunar eclipse May 4 2004-Jpeter smith
2004 May 04
Lunar eclipse from moon-2004May04
Lunar eclipse chart close-04may04
Oct 28 2004 total lunar eclipse-espenak
2004 Oct 28
Lunar eclipse from moon-2004Oct28
Lunar eclipse chart close-04oct28
141 2005 Apr 24
Lunar eclipse from moon-2005Apr24
Lunar eclipse chart close-05apr24
A partial eclipse of the moon (53370600)
2005 Oct 17
Lunar eclipse from moon-2005Oct17
Lunar eclipse chart close-2005Oct17
Last set 2002 Jun 24 Last set 2001 Dec 30
Next set 2006 Mar 14 Next set 2006 Sep 7
Lunar eclipse series sets from 2006–2009
Descending node   Ascending node
Saros #
and photo
Saros #
and photo
Penumbral lunar eclipse 2006 March 14 Warrenton VA
2006 Mar 14
Lunar eclipse from moon-2006Mar14
Lunar eclipse chart close-06mar14
Partial lunar eclipse Sept 7 2006-Mikelens
2006 Sep 7
Lunar eclipse from moon-2006Sep07
Lunar eclipse chart close-2006Sep07
Red moon during lunar eclipse
2007 Mar 03
Lunar eclipse from moon-2007Mar03
Lunar eclipse chart close-07mar03
Lunar Eclipse
2007 Aug 28
Lunar eclipse from moon-2007Aug28
Lunar eclipse chart close-2007aug28
February 2008 total lunar eclipse John Buonomo
2008 Feb 21
Lunar eclipse from moon-2008Feb21
Lunar eclipse chart close-08feb20
2008 Aug 16
Lunar eclipse from moon-2008Aug16
Lunar eclipse chart close-2008Aug16
Penumbral lunar eclipse Feb 9 2009 NavneethC
2009 Feb 09
Lunar eclipse from moon-2009Feb09
Lunar eclipse chart close-09feb09
Penumbral lunar eclipse Aug 6 2009 John Walker
2009 Aug 06
Lunar eclipse from moon-2009Aug06
Lunar eclipse chart close-2009aug06
Last set 2005 Apr 24 Last set 2005 Oct 17
Next set 2009 Dec 31 Next set 2009 Jul 07
Lunar eclipse series sets from 2009–2013
Ascending node   Descending node
Saros #
Saros #
110 2009 July 07
Lunar eclipse from moon-2009Jul07
Lunar eclipse chart close-2009jul07
December 2009 partrial lunar eclipse-cropped
2009 Dec 31
Lunar eclipse from moon-2009Dec31
Lunar eclipse chart close-2009Dec31
Lunar eclipse june 2010 northup
2010 June 26
Lunar eclipse from moon-2010Jun26
Lunar eclipse chart close-2010jun26
Near Greatest Eclipse 20101221 0011-crop
2010 Dec 21
Lunar eclipse from moon-2010Dec21
Lunar eclipse chart close-10dec21
Lunar eclipse June 2011 Total
2011 June 15
Lunar eclipse from moon-2011Jun15
Lunar eclipse chart close-2011jun15
Lunar eclipse by Shiny Things cropped
2011 Dec 10
Lunar eclipse from moon-2011Dec10
Lunar eclipse chart close-2011Dec10
Partial Eclipse of Moon 4th June 2012 Australia cropped
2012 June 04
Lunar eclipse from moon-2012Jun04
Lunar eclipse chart close-2012Jun04
145 2012 Nov 28
Lunar eclipse from moon-2012Nov28
Lunar eclipse chart close-2012Nov28
150 2013 May 25
Lunar eclipse from moon-2013May25
Lunar eclipse chart close-2013May25
Last set 2009 Aug 06 Last set 2009 Feb 9
Next set 2013 Apr 25 Next set 2013 Oct 18
Lunar eclipse series sets from 2013–2016
Ascending node   Descending node
Saros Viewing
Type Saros Viewing
Partial lunar eclipse 2013.04.25
2013 Apr 25
Lunar eclipse from moon-2013Apr25
Lunar eclipse chart close-2013Apr25
Penumbral Eclipse in very cloudy skies. (10354279925)
2013 Oct 18
Lunar eclipse from moon-2013Oct18
Lunar eclipse chart close-2013Oct18
Lunar eclipse April 15 2014 California Alfredo Garcia Jr1
2014 Apr 15
Lunar eclipse from moon-2014Apr15
Lunar eclipse chart close-2014Apr15
Lunar eclipse October 8 2014 California Alfredo Garcia Jr mideclipse
2014 Oct 08
Lunar eclipse from moon-2014Oct08
Lunar eclipse chart close-2014Oct08
Lunar eclipse April 4 2015 greatest Alfredo Garcia Jr LA
2015 Apr 04
Lunar eclipse from moon-2015Apr04
Lunar eclipse chart close-2015Apr04
Lunar eclipse September 27 2015 greatest Alfredo Garcia Jr
2015 Sep 28
Lunar eclipse from moon-2015Sep28
Lunar eclipse chart close-2015Sep28
142 2016 Mar 23
Lunar eclipse from moon-2016Mar23
Lunar eclipse chart close-2016Mar23
Partial lunar eclipse 2016.09.16
2016 Sep 16
Lunar eclipse from moon-2016Sep16
Lunar eclipse chart close-2016Sep16
Last set 2013 May 25 Last set 2012 Nov 28
Next set 2017 Feb 11 Next set 2016 Aug 18
Lunar eclipse series sets from 2016–2020
Descending node   Ascending node
Saros Date Type
Saros Date
109 2016 Aug 18
Lunar eclipse from moon-2016Aug18
Lunar eclipse chart close-2016Aug18
Penumbral lunar eclipse 2017.02.11
2017 Feb 11
Lunar eclipse from moon-2017Feb11
Lunar eclipse chart close-2017Feb11
Lunar eclipse of 2017 August 7 Kuwait
2017 Aug 07
Lunar eclipse from moon-2017Aug07
Lunar eclipse chart close-2017Aug07
Lunar eclipse January 31 2018 California Alfredo Garcia Jr mideclipse
2018 Jan 31
Lunar eclipse from moon-2018Jan31
Lunar eclipse chart close-2018Jan31
Lunar Total Eclipse on July 27, 2018 (100 2006) (43696968392) (cropped)
2018 Jul 27
Lunar eclipse from moon-2018Jul27
Lunar eclipse chart close-2018Jul27
134 2019 Jan 21
Lunar eclipse from moon-2019Jan21
Lunar eclipse chart close-2019Jan21
139 2019 Jul 16
Lunar eclipse from moon-2019Jul16
Lunar eclipse chart close-2019Jul16
144 2020 Jan 10
Lunar eclipse from moon-2020Jan10
Lunar eclipse chart close-2020Jan10
149 2020 Jul 05
Lunar eclipse from moon-2020Jul05
Lunar eclipse chart close-2020Jul05
Last set 2016 Sep 16 Last set 2016 Mar 23
Next set 2020 Jun 05 Next set 2020 Nov 30

See also


  1. ^ McClure, Bruce (July 27, 2018). "Century's Longest Lunar Eclipse July 27". EarthSky. Retrieved August 1, 2018.
  2. ^ Karttunen, Hannu (2007). Fundamental Astronomy. Springer. p. 139. ISBN 9783540341444.
  3. ^ "Observing Blog - In Search of Selenelion". Sky & Telescope. 2010-06-26. Retrieved 2011-12-08.
  4. ^ Clarke, Kevin. "On the nature of eclipses". Inconstant Moon. Cyclopedia Selenica. Retrieved 19 December 2010.
  5. ^ Paul Deans and Alan M. MacRobert (July 16, 2006). "Observing and Photographing Lunar Eclipses". Sky & Telescope. F+W.
  6. ^ Fred Espenak and Jean Meeus. "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.
  7. ^ 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.
  8. ^ Pollack, Rebecca. "Ancient Myths Revised with Lunar Eclipse". University of Maryland. Retrieved 2 October 2014.
  9. ^ Ani. "Hindus take a dip in the Ganges during Lunar Eclipse". Yahoo News. Retrieved 2 October 2014.
  10. ^ a b Lee, Jane. "Lunar Eclipse Myths From Around the World". National Geographic. Retrieved 9 October 2014.
  11. ^ Quilas, Ma Evelyn. "Interesting Facts and Myths about Lunar Eclipse". LA Times. Retrieved 2 October 2014.
  13. ^ Kaul, Gayatri. "What Lunar Eclipse Means in Different Parts of the World". Retrieved 6 October 2014.
  14. ^ a b Sappenfield, Mark (13 April 2014). "Blood Moon to arrive Monday night. What is a Blood Moon?". Christian Science Monitor. Retrieved 8 February 2018.
  15. ^ 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.
  16. ^ "All you need to know about the 'blood moon'". theguardian. 28 September 2015.
  17. ^ a b "What is a Blood Moon?". Earth & Sky. 24 April 2014. Retrieved 30 May 2014.
  18. ^ Bailey, Sarah Pulliam (15 April 2014). "'Blood moon' sets off apocalyptic debate among some Christians". Washington Post. Religion News Service. Retrieved 8 February 2018.
  19. ^ "Lunar Eclipse @ ESO". European Southern Observatory. Retrieved 14 August 2017.

Further reading

  • Bao-Lin Liu, Canon of Lunar Eclipses 1500 B.C.-A.D. 3000, 1992
  • Jean Meeus and Hermann Mucke Canon of Lunar Eclipses. Astronomisches Büro, Vienna, 1983
  • Espenak, F., Fifty Year Canon of Lunar Eclipses: 1986–2035. NASA Reference Publication 1216, 1989

External links

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