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Lunar eclipse

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									Lunar eclipse
From Wikipedia, the free encyclopedia
For other uses, see Lunar eclipse (disambiguation).
Not to be confused with Solar eclipse.




The June 2011 total eclipse

A lunar eclipse occurs when the Moon passes behind the Earth so 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, a lunar eclipse can only occur the night of a full
moon. The type and length of an eclipse depend upon the Moon's location relative to its orbital nodes.
The most recent total lunar eclipse occurred on December 10, 2011. The previous total lunar
eclipse occurred on June 15, 2011; The recent eclipse was visible from all of Asia and Australia, seen
as rising over Europe and setting over Northwest North America. The last to previous total lunar
eclipse occurred on December 21, 2010, at 08:17 UTC.[1]

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, 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 no brighter (indeed dimmer) than the full moon
itself.

                   Contents
                     [hide]
            1 Types of lunar eclipse

     o                   1.1 Selenelion

     o                   1.2 Danjon scale

            2 Eclipse cycles

            3 Recent and forthcoming lunar eclipse
    events

            4 Gallery

            5 Lunar eclipse in Mythology

            6 See also

            7 References

            8 Further reading

            9 External links

    Types of lunar eclipse




    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.

    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. Apenumbral 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.




As seen by an observer on Earth on the imaginarycelestial 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.

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 atotal 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 4 hours.[2] 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 appreciably within the changes in the orbital distance of the moon. Thus, a totally
eclipsed Moon occurring near apogee will lengthen the duration of totality.
The timing of total lunar eclipses are determined by its contacts:[3]

         P1 (First contact): Beginning of the penumbral eclipse. The Earth's penumbra touches the
         Moon's outer limb.

         U1 (Second contact): Beginning of the partial eclipse. The Earth's umbra touches the Moon's
         outer limb.

         U2 (Third contact): Beginning of the total eclipse. The Moon's surface is entirely within the
         Earth's umbra.

         Greatest eclipse: The peak stage of the total eclipse. The Moon is at its closest to the center
         of the Earth's umbra.

         U3 (Fourth contact): End of the total eclipse. The Moon's outer limb exits the Earth's umbra.

         U4 (Fifth contact): End of the partial eclipse. The Earth's umbra leaves the Moon's surface.

         P2 (Sixth contact): End of the penumbral eclipse. The Earth's shadow no longer makes any
         contact with the Moon.
                                  Selenelion
                                  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 umbra, the Sun and the eclipsed Moon can both be seen
                                  at the same time because the umbra is bigger than the moon, and
                                  because the refraction of light through the Earth’s atmosphere causes
                                  each of them to appear higher in the sky than their true geometric
                                  position.[4]

                                  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 air
                        molecules and the small particles, and so by the time the light has
                        passed through the atmosphere, the longer wavelengths dominate.
                        This resulting light we perceive asred. 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:[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.
                                                Eclipse cycles

                                                See also: Saros (astronomy) and Eclipse cycle

                                                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.

Recent and forthcoming lunar
eclipse events

   March 3, 2007, lunar eclipse ― The first
    total lunar eclipse of 2007 occurred on
    March 3, 2007, and was partially visible
    from the Americas, Asia and Australia. The
    complete event was visible
    throughout Africaand Europe. The event
    lasted seventy-five minutes, began at
    20:16 UTC, and reached totality at
    22:43 UTC.[6]

   August 2007 lunar eclipse ― August 28,
    2007, saw the second total lunar eclipse of
    the year. The initial stage began at
    07:52 UTC, and reached totality at
    09:52 UTC. This eclipse was viewable form
    Eastern Asia, Australia and New
    Zealand the Pacific, and the Americas.[7]

   February 2008 lunar eclipse ― The only
    total lunar eclipse of 2008 occurred on
    February 21, 2008, beginning at
    01:43 UTC, visible from Europe, the
    Americas, and Africa.[8]

   There was a partial eclipse of the Moon
    on December 31, 2009.

   There was a partial eclipse of the Moon
    on June 26, 2010.

   There was a total eclipse of the Moon
    on December 21, 2010.

   There was a total eclipse of the Moon
    on June 15, 2011.
   There was a total eclipse of the Moon
    on December 10, 2011.
Gallery
See also
        Moon portal



   Lunar eclipses in history

          May 1453 lunar eclipse - Fall of
           Constantinople

          March 1504 lunar eclipse - Columbus’
           lunar eclipse

          December 1573 lunar eclipse - Tycho
           Brahe

   Eclipse

   Moon illusion

   Orbit of the Moon

    List of lunar eclipsesDecember 21, 2010
    Lunar Eclipse




    




    This diagram shows how the moon appears

    reddish orange during a lunar eclipse.
        




     Painting by Lucien Rudaux, showing what a

     lunar eclipse might look like when viewed

     from the surface of the moon. The moon's

     surface appears red because the only

     sunlight available is refracted through the

     Earth's atmosphere on the edges of the

     earth, as shown in the sky in this painting.

Lunar eclipse in Mythology

Several cultures have myths related to lunar
eclipses. 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.[9]




								
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