Eclipse
9770
225720616
2008-07-15T02:03:24Z
Khunglongcon
6358314
{{Otheruses1|astronomical eclipses}}
{{Redirect|Total eclipse||Total Eclipse (disambiguation)}}
[[Image:Solar eclipse from space 29 Mar 2006.jpg|right|thumb|280px|This view from the [[International Space Station]] shows the shadow of the Moon cast upon the eastern [[Mediterranean Sea]] near [[Cyprus]]. ''[[NASA]] image.'']]
An '''eclipse''' is an astronomical event that occurs when one [[celestial object]] moves into the shadow of another. The term is derived from the [[ancient Greek]] noun {{lang|grc|έκλειψις}} (''{{lang|grc-Latn|ékleipsis}}''), from verb {{lang|grc|εκλείπω}} (''{{lang|grc-Latn|ekleípō}}''), "I cease to exist," a combination of prefix {{lang|grc|εκ-}} (''{{lang|grc-Latn|ek-}}''), from preposition {{lang|grc|εκ, εξ}} (''{{lang|grc-Latn|ek, ex}}''), "out," and of verb {{lang|grc|λείπω}} (''{{lang|grc-Latn|leípō}}''), "I am absent".<ref>{{cite web
| last=Liddell | hry gerg
| coauthors=Scott, Robert | year=1940
| url=http://www.perseus.tufts.edu/cgi-bin/ptext?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3D%2332334
| title=A Greek-English Lexicon
| publisher=The National Science Foundation
| accessdate=2007-12-13 }}</ref>
When an eclipse occurs within a stellar system, such as the [[Solar System]], it forms a type of [[syzygy]]—the alignment of three or more celestial bodies in the same [[gravity|gravitational]] system along a straight line.<ref>{{cite press release
| author=Staff | date=[[March 31]], [[1981]]
| publisher=The New York Times
| title=Science Watch: A Really Big Syzygy
| url=http://query.nytimes.com/gst/fullpage.html?sec=health&res=9F02E5DB1039F932A05750C0A967948260&fta=y
| accessdate=2008-02-29 }}</ref>
The term eclipse is most often used to describe either a [[solar eclipse]], when the Moon's shadow crosses the Earth's surface, or a [[lunar eclipse]], when the Moon moves into the shadow of Earth. However, it can also refer to such events beyond the Earth-Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its parent planet, or a moon passing into the shadow of another moon. A [[binary star]] system can also produce eclipses if the plane of their orbit intersects the position of the observer.
==Syzygy==
[[Image:Umbra01.svg|right|thumb|Umbra and penumbra cast by a solid object occulting a light source.]]
An eclipse occurs when there is a linear arrangement between a star and two celestial bodies, such as a planet and a moon. The shadow cast by the object closest to the star intersects the more distant body, lowering the amount of luminosity reaching the latter's surface. The region of shadow cast by the occulting body is divided into an [[umbra]], where the radiation from the star's [[photosphere]] is completely blocked, and a [[penumbra]], where only a portion of the radiation is blocked.<ref name=glossary>{{cite web
| last=Espenak | first=Fred | date=[[September 21]], [[2007]]
| url=http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/SEglossary.html
| title=Glossary of Solar Eclipse Terms
| publisher=NASA | accessdate=2008-02-28 }}</ref>
A total eclipse will occur when the observer is located within the umbra of the [[Occultation|occulting]] object. Totality occurs at the point of maximum phase during a total eclipse, when the occulted object is the most completely covered. Outside the umbra, the occulting object only partially covers the light source and this produces a partial eclipse. The part of the occulting object's shadow that extends beyond the umbra is called the antumbra. For observer inside the antumbra of a [[solar eclipse]], the [[Moon]] appears smaller than the [[Sun]].<ref name=glossary/>
For spherical bodies, when the occluding object is smaller than the star, the umbra forms a cone whose length (''L'') is given by:
:<math>L\ =\ \frac{r \cdot R_o}{R_s - R_o}</math>
where ''R<sub>s</sub>'' is the radius of the star, ''R<sub>o</sub>'' is the occulting object's radius, and ''r'' is the distance from the star to the occulting object. For [[Earth]], on average ''L'' is equal to 1.384{{e|6}} [[kilometer|km]], which is much larger than the Moon's [[semimajor axis]] of 3.844{{e|5}} km. Hence the umbral cone of the Earth can completely envelop the Moon during a [[lunar eclipse]].<ref>{{cite book
| first=Robin M. | last=Green | year=1985
| title=Spherical Astronomy | publisher=Oxford University Press
| isbn=0521317797 }}</ref> If the occulting object has an atmosphere, however, some of the luminosity of the star can be [[refraction|refracted]] into the volume of the umbra. This occurs, for example, during an eclipse of the Moon by the Earth—producing a faint, ruddy illumination of the Moon even at totality.
An [[astronomical transit]] is also a type of syzygy, but is used to describe the situation where the nearer object is considerably smaller in apparent size than the more distant object. Likewise, an [[occultation]] is a syzygy where the apparent size of the nearer object appears much larger than the distant object, and the distant object becomes completely hidden during the event.
An [[eclipse cycle]] takes place when a series of eclipses are separated by a certain interval of time. This happens when the orbital motions of the bodies form repeating harmonic patterns. A particular instance is the [[Saros cycle]], which results in a repetition of a solar or lunar eclipse every 6,585.3 days, or a little over 18 years. However, because this cycle has an odd number of days, a successive eclipse is viewed from a different part of the world.<ref>{{cite web
| last=Espenak | first=Fred | date=[[July 12]], [[2007]]
| url=http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html
| title=Eclipses and the Saros
| publisher=NASA | accessdate=2007-12-13 }}</ref>
==Earth-Moon System==
An eclipse involving the Sun, Earth and Moon can occur only when they are nearly in a straight line, allowing the shadow cast by the Sun to fall upon the eclipsed body. Because the [[orbit of the Moon|orbital plane of the Moon]] is tilted with respect to the orbital plane of the Earth (the [[ecliptic]]), eclipses can occur only when the Moon is close to the intersection of these two planes (the [[node (astronomy)|node]]s). The Sun, Earth and nodes are aligned twice a year, and eclipses can occur during a period of about two months around these times. There can be from four to seven eclipses in a calendar [[year]], which repeat according to various [[eclipse cycle]]s, such as the [[Saros cycle]].
===Solar eclipse===
{{main|Solar eclipse}}
An eclipse of the Sun by the Moon is termed a solar eclipse. Records of solar eclipses have been kept since ancient times. A [[Syria]]n clay tablet records a solar eclipse on March 5, 1223 BCE,<ref>{{cite journal
| last=de Jong | first=T. | coauthors=van Soldt, W. H.
| title=The earliest known solar eclipse record redated
| journal=Nature | year=1989 | volume=338 | pages=238–240
| url=http://www.nature.com/nature/journal/v338/n6212/abs/338238a0.html
| accessdate=2007-05-02
| doi=10.1038/338238a0 }}</ref> while Paul Griffin argues that a stone in Ireland records an eclipse on November 30, 3340 BCE.<ref>{{cite web
| last=Griffin | first=Paul | year=2002
| url =http://www.astronomy.ca/3340eclipse/
| title =Confirmation of World's Oldest Solar Eclipse Recorded in Stone
| publisher =The Digital Universe
| accessdate =2007-05-02
}}</ref> Chinese historical records of solar eclipses date back
over 4,000 years and have been used to measure changes in the
Earth's rate of spin.<ref>{{cite web
| url =http://www.bibalex.org/eclipse2006/HistoricalObservationsofSolarEclipses.htm
| title=Solar Eclipses in History and Mythology
| publisher=Bibliotheca Alexandrina | accessdate=2007-05-02
}}</ref> Eclipse dates can also be used for chronological dating
of historical records.
[[Image:Solar eclips 1999 4.jpg|thumb|250px|right|Totality during the [[1999]] solar eclipse. [[Solar prominence]]s can be seen along the limb (in red) as well as extensive [[corona]]l filaments.]]
The type of solar eclipse event depends on the distance of the Moon from the Earth during the event. A total solar eclipse occurs when the Earth intersects the umbra portion of the Moon's shadow. When the umbra does not reach the surface of the Earth, the Sun is only partially occluded, resulting in an annular eclipse. Partial solar eclipses occur when the viewer is inside the penumbra.<ref name="cardall_daunt">{{cite web
| first=C. Y. | last=Cardall | coauthors=Daunt, S. J. | year=1999
| url= http://astrogeology.usgs.gov/HotTopics/index.php?/archives/147-Names-for-the-Columbia-astronauts-provisionally-approved.html
| title=Solar Eclipses | publisher =University of Tennessee
| accessdate=2007-04-29 }}</ref>
Solar eclipses are relatively brief events that can only be viewed in totality along a relatively narrow track. Under the most favorable circumstances, a total solar eclipse can last for 7 minutes, 31 seconds, and can be viewed along a track that is up to 250 km wide. However, the region where a partial eclipse can be observed is much larger. The Moon's umbra will advance eastward at a rate of 1,700 km/h, until it no longer intersects the Earth.
During a solar eclipse, the Moon can sometimes perfectly cover the Sun because its apparent size is nearly the same as the Sun when viewed from the Earth. A solar eclipse is actually a misnomer; the phenomenon is more correctly described as an [[occultation]] of the Sun by the Moon or an eclipse of the Earth by the Moon.
===Lunar eclipse===
{{main|Lunar eclipse}}
[[Image:Eclipse lune.jpg|thumb|250px|right|The progression of a lunar eclipse. Totality is shown with the last two images to lower right. These required a longer exposure time to make the details visible.]]
Lunar eclipses occur when the Moon passes through the Earth's shadow. Since this occurs only when the Moon is on the far side of the Earth from the Sun, lunar eclipses only occur when there is a [[full moon]]. Unlike a solar eclipse, an eclipse of the Moon can be observed from nearly an entire hemisphere. For this reason it is much more common to observe a lunar eclipse from a given location. A lunar eclipse also lasts longer, taking several hours to complete, with totality itself usually averaging anywhere from about 30 minutes to over an hour.<ref>{{cite web
| author=Staff | date=[[January 6]], [[2006]]
| url=http://www.crh.noaa.gov/fsd/astro/suneclipse.php
| title=Solar and Lunar Eclipses
| publisher=NOAA | accessdate =2007-05-02 }}</ref>
There are three types of lunar eclipses: penumbral, when the Moon crosses only the Earth's penumbra; partial, when the Moon crosses partially into the Earth's [[umbra]]; and total, when the Moon circles entirely within the Earth's umbra. Total lunar eclipses pass through all three phases. Even during a total lunar eclipse, however, the Moon is not completely dark. Sunlight refracted through the Earth's atmosphere intersects the umbra and provides a faint illumination. Much as in a sunset, the atmosphere tends to scatter light with shorter wavelengths, so the illumination of the Moon by refracted light has a red hue.<ref>
{{cite web
| last=Phillips | first=Tony | date=[[February 13]], [[2008]]
| url =http://science.nasa.gov/headlines/y2008/13feb_lunareclipse.htm
| title=Total Lunar Eclipse
| publisher=NASA | accessdate=2008-03-03 }}</ref>
==Other planets==
{{main|Transit of Phobos from Mars|Solar eclipses on Jupiter|Solar eclipses on Pluto}}
[[Image:PIA05553.gif|right|thumbnail|[[Transit of Phobos from Mars|Phobos transits Sun]], as seen by Mars Rover ''[[MER-B|Opportunity]]'']]
[[Image:JupiterandIo.jpg|thumb|right|A picture of [[Jupiter]] and its moon [[Io (moon)|Io]] taken by [[Hubble Space Telescope|Hubble]]. The black spot is Io's shadow.]]
[[Image:Saturn eclipse.jpg|250px|right|thumb|[[Saturn]] eclipses the Sun as seen from the [[Cassini–Huygens]] space probe]]
Eclipses are impossible on [[Mercury (planet)|Mercury]] and [[Venus]], which have no moons. However, both have been observed to transit across the face of the Sun. There are on average 13 transits of Mercury each century. Transits of Venus occur in pairs separated by an interval of eight years, but each pair of events happen less than once a century.<ref>{{cite web
| last=Espenak | first=Fred | date=[[May 29]], [[2007]]
| url=http://sunearth.gsfc.nasa.gov/eclipse/transit/transit.html
| title=Planetary Transits Across the Sun
| publisher=NASA | accessdate=2008-03-11 }}</ref>
On [[Mars]], only partial solar eclipses are possible, because neither of its moons is large enough, at their respective orbital radii, to cover the Sun's disc as seen from the surface of the planet. Eclipses of the moons by Mars are not only possible, but commonplace, with hundreds occurring each Earth year. There are also rare occasions when Deimos is eclipsed by Phobos.<ref>{{cite book
| first=Norman | last=Davidson | year=1985
| title=Astronomy and the Imagination: A New Approach to Man's Experience of the Stars
| publisher=Routledge
| id=ISBN 0710203713 }}</ref> Martian eclipses have been photographed from both the surface of Mars and from orbit.
The [[gas giant]] planets ([[Jupiter]],<ref name=CallistoSun>{{cite web
|date = 2009-Jun-03 00:28 UT
|title = Start eclipse of the Sun by Callisto from the center of Jupiter
|publisher = [http://space.jpl.nasa.gov/ JPL Solar System Simulator]
|url = http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=504&vbody=599&month=6&day=3&year=2009&hour=00&minute=20&fovmul=1&rfov=0.5&bfov=30&brite=1
|accessdate = 2008-06-05}}</ref> [[Saturn]],<ref name=TitanSun>{{cite web
|date = 2009-Aug-03 02:46 UT
|title = Eclipse of the Sun by Titan from the center of Saturn
|publisher = [http://space.jpl.nasa.gov/ JPL Solar System Simulator]
|url = http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=606&vbody=699&month=8&day=3&year=2009&hour=02&minute=46&fovmul=1&rfov=5&bfov=30&porbs=1&brite=1
|accessdate = 2008-06-05}}</ref> [[Uranus]],<ref name=MirandaSun>{{cite web
|date = 2007-Jan-22 19:58 UT (JPL Horizons S-O-T=0.0565)
|title = Brief Eclipse of the Sun by Miranda from the center of Uranus
|publisher = [http://space.jpl.nasa.gov/ JPL Solar System Simulator]
|url = http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=705&vbody=799&month=1&day=22&year=2007&hour=19&minute=59&fovmul=1&rfov=2&bfov=30&porbs=1&brite=1
|accessdate = 2008-06-05}}</ref> and [[Neptune]])<ref name=NereidSun>{{cite web
|date = 2006-Mar-28 20:19 UT (JPL Horizons S-O-T=0.0079)
|title = Transit of the Sun by Nereid from the center of Neptune
|publisher = [http://space.jpl.nasa.gov/ JPL Solar System Simulator]
|url = http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=802&vbody=899&month=3&day=28&year=2006&hour=20&minute=40&fovmul=1&rfov=0.05&bfov=30&porbs=1&brite=1
|accessdate = 2008-06-05}}</ref> have many moons and thus frequently display eclipses. The most striking involve [[Jupiter]], which has four large moons and a low [[axial tilt]], making eclipses more frequent as these bodies pass through the shadow of the larger planet. Transits occur with equal frequency. It is common to see the larger moons casting circular shadows upon Jupiter's cloudtops.
The eclipses of the [[Galilean moon]]s by Jupiter became accurately predictable once their orbital elements were known. During the 1670s, it was discovered that these events were occurring about 17 minutes later than expected when Jupiter was on the far side of the Sun. [[Ole Rømer]] deduced that the delay was caused by the time needed for light to travel from Jupiter to the Earth. This was used to produce the first estimate of the [[speed of light]].<ref>{{cite web
| url = http://www.mathpages.com/home/kmath203/kmath203.htm
| title = Roemer's Hypothesis
| publisher = MathPages
| accessdate = 2007-01-12 }}</ref>
On the other three [[gas giant]]s, eclipses only occur at certain periods during the planet's orbit, due to their higher [[inclination]] between the orbits of the moon and the [[orbital plane]] of the planet. The moon [[Titan (moon)|Titan]], for example, has an orbital plane tilted about 1.6° to Saturn's equatorial plane. But Saturn has an axial tilt of nearly 27°. The orbital plane of Titan only crosses the line of sight to the Sun at two points along Saturn's orbit. As the orbital period of Saturn is 29.7 years, an eclipse is only possible about every 15 years.
The timing of the Jovian satellite eclipses was also used to calculate an observer's [[longitude]] upon the Earth. By knowing the expected time when an eclipse would be observed at a standard longitude (such as [[Greenwich]]), the time difference could be computed by accurately observing the local time of the eclipse. The time difference gives the longitude of the observer because every hour of difference corresponded to 15° around the Earth's equator. This technique was used, for example, by [[Giovanni Domenico Cassini|Giovanni D. Cassini]] in 1679 to re-map [[France]].<ref>{{cite journal
| last =Cassini
| first =Giovanni D.
| authorlink=Giovanni Domenico Cassini
| title=Monsieur Cassini His New and Exact Tables for the Eclipses of the First Satellite of Jupiter, Reduced to the Julian Stile, and Meridian of London
| journal=Philosophical Transactions
| year=1694
| volume=18
| pages=237–256
| url=http://links.jstor.org/sici?sici=0260-7085(1694)18%3C237%3AMCHNAE%3E2.0.CO%3B2-W
| accessdate=2007-04-30
| doi=10.1098/rstl.1694.0048 }}</ref>
[[Pluto]], with its proportionately large moon [[Charon (moon)|Charon]], is also the site of many eclipses. A series of such mutual eclipses occurred between 1985 and 1990.<ref>{{cite journal
| last=Buie | first=M. W. | coauthors=Polk, K. S.
| title=Polarization of the Pluto-Charon System During a Satellite Eclipse
| journal=Bulletin of the American Astronomical Society
| year=1988 | volume=20 | pages=806
| url=http://adsabs.harvard.edu/abs/1988BAAS...20..806B
| accessdate=2008-03-11 }}</ref> These daily events led to the first accurate measurements of the physical parameters of both objects.<ref>{{cite journal
| last=Tholen | first=D. J. | coauthors=Buie, M. W.; Binzel, R. P.; Frueh, M. L.
| title=Improved Orbital and Physical Parameters for the Pluto-Charon System
| journal=Science | year=1987 | volume=237
| issue=4814 | pages=512–514
| url=http://www.sciencemag.org/cgi/content/refs/237/4814/512
| accessdate=2008-03-11
| doi=10.1126/science.237.4814.512
| pmid=17730324
}}</ref>
==Eclipsing binaries==
A [[binary star]] system consists of two stars that orbit around their common [[center of mass]]. The movements of both stars lie on a common [[Orbital plane (astronomy)|orbital plane]] in space. When this plane is very closely aligned with the location of an observer, the stars can be seen to pass in front of each other. The result is a type of extrinsic [[variable star]] system called an [[eclipsing binary]].
The maximum [[luminosity]] of an eclipsing binary system is equal to the sum of the luminosity contributions from the individual stars. When one star passes in front of the other, the luminosity of the system is seen to decrease. The luminosity returns to normal once the two stars are no longer in alignment.<ref>{{cite web
| last = Bruton
| first = Dan
| url =http://www.physics.sfasu.edu/astro/ebstar/ebstar.html
| title =Eclipsing binary stars
| publisher =Midnightkite Solutions
| accessdate = 2007-05-01
}}</ref>
The first eclipsing binary star system to be discovered was [[Algol]], a star system in the constellation [[Perseus (constellation)|Perseus]]. Normally this star system has a [[visual magnitude]] of 2.1. However, every 20.867 days the magnitude decreases to 3.4 for more than 9 hours. This is caused by the passage of the dimmer member of the pair in front of the brighter star.<ref>{{cite web
| last = Price
| first = Aaron
| date = January 1999
| url =http://www.aavso.org/vstar/vsots/0199.shtml
| title =Variable Star Of The Month: Beta Persei (Algol)
| publisher =AAVSO
| accessdate = 2007-05-01
}}</ref> The concept that an eclipsing body caused these luminosity variations was introduced by [[John Goodricke]] in 1783.<ref>{{cite journal
| last = Goodricke
| first = John
| authorlink=John Goodricke
| title=Observations of a New Variable Star
| journal=Philosophical Transactions of the Royal Society of London
| year=1785
| volume=75
| pages=153–164
| url=http://adsabs.harvard.edu/abs/1785RSPT...75..153G
| accessdate=2007-05-01 }}</ref>
==See also==
* [[Eclipse cycle]]
* [[Saros cycle]]
* [[Syzygy]]
* [[Mursili's eclipse]]
==References==
{{reflist|2}}
== External links ==
{{commons|Eclipse}}
* [http://www.phys.uu.nl/~vgent/eclipse/eclipsecycles.htm A Catalogue of Eclipse Cycles]
* [http://www.hermit.org/Eclipse/when_search.shtml Search 5,000 years of eclipses] (''notice: loads slowly'')
* [http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html NASA eclipse home page]
* [http://www.eclipses.info International Astronomical Union's Working Group on Solar Eclipses]
* [http://www.markstravelnotes.com/travelogues/eclipse_chasing/ Mark's eclipse chasing website]
* [http://xjubier.free.fr/en/site_pages/SolarEclipsesGoogleMaps.html Interactive eclipse maps site]
* [http://www.totaleclipses.com Dan McGlaun's Total Eclipse web site]
* [http://www.sanskrit.org/www/Astronomy/Rahu.html Why do Hindus believe that the mythological demons Rahu and Ketu cause solar eclipses?]
* [http://dailycatholic.org/issue/05Apr/04517qui.htm May 18, 1920 5:22-5:33 eclipse John Paul II]
* [http://www.austinpowers.com/ Dr. Evils Escape Pod Eclipse Official Sight]
===Image galleries===
* [http://www.perseus.gr/Astro-Eclipses.htm Solar and Lunar Eclipse Image Gallery]
* [http://www.williams.edu/astronomy/eclipse Williams College eclipse collection of images]
* [http://www.zam.fme.vutbr.cz/~druck/Eclipse/ Prof. Druckmüller's eclipse photography site]
[[Category:Eclipses| ]]
[[Category:Astronomical events]]
[[Category:Earth phenomena]]
[[Category:Astrological aspects]]
[[ar:كسوف الشمس]]
[[bg:Затъмнение]]
[[ca:Eclipsi]]
[[cs:Zatmění Slunce]]
[[da:Solformørkelse]]
[[de:Verfinsterung]]
[[et:Päikesevarjutus]]
[[el:Έκλειψη]]
[[es:Eclipse]]
[[eo:Eklipso]]
[[eu:Eklipse]]
[[fa:خورشید گرفتگی]]
[[fr:Éclipse]]
[[fy:Sinnefertsjustering]]
[[gl:Eclipse]]
[[ko:식 (천문)]]
[[hi:ग्रहण]]
[[hr:Pomrčina]]
[[id:Gerhana]]
[[it:Eclissi]]
[[he:ליקוי מאורות]]
[[jv:Grahana srengéngé]]
[[la:Defectio solis]]
[[lv:Saules aptumsums]]
[[lb:Sonnefinsternis]]
[[lt:Užtemimas]]
[[hu:Napfogyatkozás]]
[[ml:ഗ്രഹണം]]
[[mt:Eklissi]]
[[mr:ग्रहण]]
[[ms:Gerhana]]
[[nl:Eclips]]
[[ja:食 (天文)]]
[[no:Solformørkelse]]
[[nds:Sünndüsternis]]
[[pl:Zaćmienie]]
[[pt:Eclipse]]
[[ru:Затмение]]
[[sk:Zatmenie]]
[[sl:Sončev mrk]]
[[sr:Помрачење]]
[[fi:Auringonpimennys]]
[[sv:Eklips]]
[[th:อุปราคา]]
[[tr:Güneş tutulması]]
[[uk:Затемнення]]
[[ur:سورج گرہن]]
[[vi:Nhật thực]]
[[zh:食 (天文現象)]]