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Schematic diagram of the shadow cast by the Earth. Within the central umbra shadow, the Moon is totally shielded from direct illumination by the Sun. In contrast, within the penumbra shadow, only a portion of sunlight is blocked.
As seen by an observer on Earth on the imaginary celestial sphere, the Moon crosses the ecliptic every orbit at positions called nodes twice every month. When the full moon occurs in the same position at the node, a lunar eclipse can occur. These two nodes allow two to five eclipses per year, parted by approximately six months. (Note: Not drawn to scale. The Sun is much larger and farther away than the Moon.)
A total penumbral lunar eclipse dims the moon in direct proportion to the area of the sun’s disk blocked by the earth. This comparison shows the southern shadow penumbral lunar eclipse of January 1999 (left) to the same moon outside of the shadow (right) demonstrates this subtle dimming.
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.
Painting by Lucien Rudaux (1874–1947), showing what a lunar eclipse might look like from the surface of the moon. The moon's surface appears red due to the only sunlight visible as refracted through the Earth's atmosphere on the edges of the earth in the sky

A lunar eclipse occurs when the moon passes behind the earth such that the earth blocks the sun’s rays from striking the moon. This can occur only when the Sun, Earth and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, there is always a full moon the night of a lunar eclipse. The type and length of an eclipse depend upon the Moon’s location relative to its orbital nodes. The next total lunar eclipse occurs on December 21, 2010. Unlike a solar eclipse, which can only be viewed from a certain relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of the Earth. A lunar eclipse lasts for a few hours, whereas a total solar eclipse lasts for only a few minutes at any given place.

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Types of lunar eclipses

The shadow of the Earth can be divided into two distinctive parts: the umbra and penumbra. Within the umbra, there is no direct solar radiation. However, as a result of the Sun’s large angular size, solar illumination is only partially blocked in the outer portion of the Earth’s shadow, which is given the name penumbra.

A penumbral eclipse occurs when the Moon passes through the Earth’s penumbra. The penumbra causes a subtle darkening of the Moon's surface. A special type of penumbral eclipse is a total penumbral eclipse, during which the Moon lies exclusively within the Earth’s penumbra. Total penumbral eclipses are rare, and when these occur, that portion of the Moon which is closest to the umbra can appear somewhat darker than the rest of the Moon.

A partial lunar eclipse occurs when only a portion of the Moon enters the umbra. When the Moon travels completely into the Earth’s umbra, one observes a total lunar eclipse. The Moon’s speed through the shadow is about one kilometer per second (2,300 mph), and totality may last up to nearly 107 minutes. Nevertheless, the total time between the Moon’s first and last contact with the shadow is much longer, and could last up to 3.8 hours.[1] The relative distance of the Moon from the Earth at the time of an eclipse can affect the eclipse’s duration. In particular, when the Moon is near its apogee, the farthest point from the Earth in its orbit, its orbital speed is the slowest. The diameter of the umbra does not decrease much with distance. Thus, a totally-eclipsed Moon occurring near apogee will lengthen the duration of totality.

A selenelion or selenehelion occurs when both the Sun and the eclipsed Moon can be observed at the same time. This can only happen just before sunset or just after sunrise, and both bodies will appear just above the horizon at nearly opposite points in the sky. This arrangement has led to the phenomenon being referred to as a horizontal eclipse. It happens during every lunar eclipse at all those places on the Earth where it is sunrise or sunset at the time. Indeed, the reddened light that reaches the Moon comes from all the simultaneous sunrises and sunsets on the Earth. Although the Moon is in the Earth’s geometrical shadow, the Sun and the eclipsed Moon can appear in the sky at the same time because the refraction of light through the Earth’s atmosphere causes objects near the horizon to appear higher in the sky than their true geometric position.[2]

The Moon does not completely disappear as it passes through the umbra because of the refraction of sunlight by the Earth’s atmosphere into the shadow cone; if the Earth had no atmosphere, the Moon would be completely dark during an eclipse. The red coloring arises because sunlight reaching the Moon must pass through a long and dense layer of the Earth’s atmosphere, where it is scattered. Shorter wavelengths are more likely to be scattered by the small particles, and so by the time the light has passed through the atmosphere, the longer wavelengths dominate. This resulting light we perceive as red. This is the same effect that causes sunsets and sunrises to turn the sky a reddish color; an alternative way of considering the problem is to realize that, as viewed from the Moon, the Sun would appear to be setting (or rising) behind the 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.

Danjon scale

The following scale (the Danjon scale) was devised by André Danjon for rating the overall darkness of lunar eclipses:[3]

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.

Eclipse cycles

Every year there are at least two lunar eclipses, although total lunar eclipses are significantly less common. If one knows the date and time of an eclipse, it is possible to predict the occurrence of other eclipses using an eclipse cycle like the Saros cycle.

Recent and forthcoming lunar eclipse events

1995-1998

Lunar eclipse series sets from 1995-1998
Ascending node   Descending node
Saros
Photo
Date
Viewing
Type
Chart
Saros
Photo
Date
Viewing
Type
Chart
112 1995 Apr 15
Lunar eclipse from moon-1995Apr15.png
Partial
Lunar eclipse chart close-1995Apr15.png
117 1995 Oct 08
Lunar eclipse from moon-1995Oct08.png
Penumbral
Lunar eclipse chart close-1995Oct08.png
122 1996 Apr 04
Lunar eclipse from moon-1996Apr04.png
Total
Lunar eclipse chart close-1996Apr04.png
127 1996 Sep 27
Lunar eclipse from moon-1996Sep27.png
Total
Lunar eclipse chart close-1996Sep27.png
132
March 1997 partial lunar eclipse 445UT-dale ireland.png
1997 Mar 24
Lunar eclipse from moon-1997Mar24.png
Partial
Lunar eclipse chart close-1997Mar24.png
137 1997 Sep 16
Lunar eclipse from moon-1997Sep16.png
Total
Lunar eclipse chart close-1997Sep16.png
142 1998 Mar 13
Lunar eclipse from moon-1998Mar13.png
Penumbral
Lunar eclipse chart close-1998Mar13.png
147 1998 Sep 06
Lunar eclipse from moon-1998Sep06.png
Penumbral
Lunar eclipse chart close-1998Sep06.png
Last set 1994 May 25 Last set 1994 Nov 18
Next set 1999 Jan 31 Next set 1998 Aug 08

1998-2002

Lunar eclipse series sets from 1998-2002
Descending node   Ascending node
Saros Date
Viewing
Type
Chart
Saros Date
Viewing
Type
Chart
109 1998 Aug 08
Lunar eclipse from moon-1998Aug08.png
Penumbral
Lunar eclipse chart close-1998Aug08.png
114 1999 Jan 31
Lunar eclipse from moon-1999Jan31.png
Penumbral
Lunar eclipse chart close-1999Jan31.png
119 1999 Jul 28
Lunar eclipse from moon-1999Jul28.png
Partial
Lunar eclipse chart close-1999Jul28.png
124 2000 Jan 21
Lunar eclipse from moon-2000Jan21.png
Total
Lunar eclipse chart close-2000Jan21.png
129 2000 Jul 16
Lunar eclipse from moon-2000Jul16.png
Total
Lunar eclipse chart close-2000jul16.png
134 2001 Jan 09
Lunar eclipse from moon-2001Jan09.png
Total
Lunar eclipse chart close-2001Jan09.png
139 2001 Jul 05
Lunar eclipse from moon-2001Jul05.png
Partial
Lunar eclipse chart close-2001Jul05.png
144 2001 Dec 30
Lunar eclipse from moon-2001Dec30.png
Penumbral
Lunar eclipse chart close-2001Dec30.png
149 2002 Jun 24
Lunar eclipse from moon-2002Jun24.png
Penumbral
Lunar eclipse chart close-2002Jun24.png
Last set 1998 Sep 06 Last set 1998 Mar 13
Next set 2002 May 26 Next set 2002 Nov 20

2002–2005

Lunar eclipse series sets from 2002–2005
Descending node   Ascending node
Saros
Photo
Date
View
Type
Chart
Saros
Photo
Date
View
Type
Chart
111 2002 May 26
Lunar eclipse from moon-2002May26.png
penumbral
Lunar eclipse chart close-2002May26.png
116 2002 Nov 20
Lunar eclipse from moon-2002Nov20.png
penumbral
Lunar eclipse chart close-2002Nov20.png
121
Lunar eclipse May 2003-TLR75.jpg
2003 May 16
Lunar eclipse from moon-2003May16.png
total
Lunar eclipse chart close-03may16.png
126
Lunar eclipse November 2003-TLR63.jpg
2003 Nov 09
Lunar eclipse from moon-2003Nov09.png
total
Lunar eclipse chart close-03nov09.png
131
Total lunar eclipse May 4 2004-Jpeter smith.jpg
2004 May 04
Lunar eclipse from moon-2004May04.png
total
Lunar eclipse chart close-04may04.png
136
Oct 28 2004 total lunar eclipse-espenak.png
2004 Oct 28
Lunar eclipse from moon-2004Oct28.png
total
Lunar eclipse chart close-04oct28.png
141
Penumbral eclipse Minneapolis 24 April 2005.png
2005 Apr 24
Lunar eclipse from moon-2005Apr24.png
penumbral
Lunar eclipse chart close-05apr24.png
146 2005 Oct 17
Lunar eclipse from moon-2005Oct17.png
partial
Lunar eclipse chart close-2005Oct17.png
Last set 2002 Jun 24 Last set 2001 Dec 30
Next set 2006 Mar 14 Next set 2006 Sep 7

2006–2009

Lunar eclipse series sets from 2006–2009
Descending node   Ascending node
Saros
Photo
Date
Viewing
Type
Chart
Saros
Photo
Date
Viewing
Type
Chart
113
Penumbral lunar eclipse 2006 March 14 Warrenton VA.jpg
2006 Mar 14
Lunar eclipse from moon-2006Mar14.png
penumbral
Lunar eclipse chart close-06mar14.png
118
Partial lunar eclipse Sept 7 2006-Mikelens.jpg
2006 Sep 7
Lunar eclipse from moon-2006Sep07.png
partial
Lunar eclipse chart close-2006Sep07.png
123
IMG 2674 copy2.jpg
2007 Mar 03
Lunar eclipse from moon-2007Mar03.png
total
Lunar eclipse chart close-07mar03.png
128
Lunar Eclipse.jpg
2007 Aug 28
Lunar eclipse from moon-2007Aug28.png
total
Lunar eclipse chart close-2007aug28.png
133
February 2008 total lunar eclipse John Buonomo.jpg
2008 Feb 21
Lunar eclipse from moon-2008Feb21.png
total
Lunar eclipse chart close-08feb20.png
138
20080816eclipsed2.jpg
2008 Aug 16
Lunar eclipse from moon-2008Aug16.png
partial
Lunar eclipse chart close-2008Aug16.png
143
Penumbral lunar eclipse Feb 9 2009 NavneethC.jpg
2009 Feb 9
Lunar eclipse from moon-2009Feb09.png
penumbral
Lunar eclipse chart close-09feb09.png
148
Penumbral lunar eclipse Aug 6 2009 John Walker.gif
2009 Aug 06
Lunar eclipse from moon-2009Aug06.png
penumbral
Lunar eclipse chart close-2009aug06.png
Last set 2005 Apr 24 Last set 2005 Oct 17
Next set 2009 Dec 31 Next set 2009 Jul 07

2009–2013

Lunar eclipse series sets from 2009–2013
Ascending node   Descending node
Saros Date
Viewing
Type
chart
Saros Date
Viewing
Type
chart
110 2009 July 07
Lunar eclipse from moon-2009Jul07.png
penumbral
Lunar eclipse chart close-2009jul07.png
115
December 2009 partrial lunar eclipse-cropped.png
2009 Dec 31
Lunar eclipse from moon-2009Dec31.png
partial
Lunar eclipse chart close-2009Dec31.png
120 2010 June 26
Lunar eclipse from moon-2010Jun26.png
partial
Lunar eclipse chart close-2010jun26.png
125 2010 Dec 21
Lunar eclipse from moon-2010Dec21.png
total
Lunar eclipse chart close-10dec21.png
130 2011 June 15
Lunar eclipse from moon-2011Jun15.png
total
Lunar eclipse chart close-2011jun15.png
135 2011 Dec 10
Lunar eclipse from moon-2011Dec10.png
total
Lunar eclipse chart close-2011Dec10.png
140 2012 June 04
Lunar eclipse from moon-2012Jun04.png
partial
Lunar eclipse chart close-2012Jun04.png
145 2012 Nov 28
Lunar eclipse from moon-2012Nov28.png
penumbral
Lunar eclipse chart close-2012Nov28.png
150 2013 May 25
Lunar eclipse from moon-2013May25.png
penumbral
Lunar eclipse chart close-2013May25.png
Last set 2009 Aug 06 Last set 2009 Feb 9
Next set 2013 Apr 25 Next set 2013 Oct 18

2013–2016

Lunar eclipse series sets from 2013–2016
Ascending node   Descending node
Saros Date
Viewing
Type Saros Date
Viewing
Type
112 2013 Apr 25
Lunar eclipse from moon-2013Apr25.png
Partial
Lunar eclipse chart close-2013Apr25.png
117 2013 Oct 18
Lunar eclipse from moon-2013Oct18.png
Penumbral
Lunar eclipse chart close-2013Oct18.png
122 2014 Apr 15
Lunar eclipse from moon-2014Apr15.png
Total
Lunar eclipse chart close-2014Apr15.png
127 2014 Oct 08
Lunar eclipse from moon-2014Oct08.png
Total
Lunar eclipse chart close-2014Oct08.png
132 2015 Apr 04
Lunar eclipse from moon-2015Apr04.png
Total
Lunar eclipse chart close-2015Apr04.png
137 2015 Sep 28
Lunar eclipse from moon-2015Sep28.png
Total
Lunar eclipse chart close-2015Sep28.png
142 2016 Mar 23
Lunar eclipse from moon-2016Mar23.png
Penumbral
Lunar eclipse chart close-2016Mar23.png
147 2016 Sep 16
Lunar eclipse from moon-2016Sep16.png
Penumbral
Lunar eclipse chart close-2016Sep16.png
Last set 2013 May 25 Last set 2012 Nov 28
Next set 2017 Feb 31 Next set 2016 Aug 08

2016–2020

Lunar eclipse series sets from 2016–2020
Descending node   Ascending node
Saros Date Type
Viewing
Saros Date
Viewing
Type
Chart
109 2016 Aug 18
Lunar eclipse from moon-2016Aug18.png
Penumbral
Lunar eclipse chart close-2016Aug18.png
114 2017 Feb 11
Lunar eclipse from moon-2017Feb11.png
Penumbral
Lunar eclipse chart close-2017Feb11.png
119 2017 Aug 07
Lunar eclipse from moon-2017Aug07.png
Partial
Lunar eclipse chart close-2017Aug07.png
124 2018 Jan 31
Lunar eclipse from moon-2018Jan31.png
Total
Lunar eclipse chart close-2018Jan31.png
129 2018 Jul 27
Lunar eclipse from moon-2018Jul27.png
Total
Lunar eclipse chart close-2018jul27.png
134 2019 Jan 21
Lunar eclipse from moon-2019Jan21.png
Total
Lunar eclipse chart close-2019Jan21.png
139 2019 Jul 16
Lunar eclipse from moon-2019Jul16.png
Partial
Lunar eclipse chart close-2019Jul16.png
144 2020 Jan 10
Lunar eclipse from moon-2020Jan10.png
Penumbral
Lunar eclipse chart close-2020Jan10.png
149 2020 Jul 05
Lunar eclipse from moon-2020Jul05.png
Penumbral
Lunar eclipse chart close-2020Jul05.png
Last set 2016 Sep 16 Last set 2016 Mar 23
Next set 2020 Jun 05 Next set 2020 Nov 30

See also

References

  • 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


Simple English

File:2007-03-03 - Lunar Eclipse small-43img.gif
A film showing the effect of a lunar eclipse. The film was made at the eclipse of March 3, 2007
File:Lunar eclipse with
When a total lunar eclipse occurs, more stars can be seen near the moon

A Lunar eclipse is an astronomical phenomenon. It occurs when the moon passes through the shadow of the Earth. Lunar eclipses occur about twice a year, much more often than solar eclipses. They also last longer than solar eclipses.

During a lunar eclipse, the Moon appears a reddish-brown color. You would probably think that the moon would be completely black because of Earth's shadow, but the reddish-brown color is due to the fact that the Sun's light reflects off Earth, and is barely visible on the Moon.

Like solar eclipses, there are different types of lunar eclipses. There are total eclipses, where all of the moon appears reddish-brown, and partial ones, where only part of the moon appears reddish-brown.

Lunar eclipses are not as rare as solar eclipses and are sometimes called the 'Yellow Moon' although it does not look as yellow.









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