The Great Comet-Aefie

8/3/2019 The Great Comet-Aefie

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THE GREAT COMET

BY MOHD. TANSRIB TAHA

SAPRI SALAM

AEFFIE CHARL CHIN

AMIRUL ASYRAF

Comet Hale-Bopp, as seen on 29 March 1997 inPazin,Croatia.

A comet is an icy small Solar System body that, when close enough to the Sun, displays

a visible coma(a thin, fuzzy, temporary atmosphere), and sometimes also a tail. Thesephenomena are both due to the effects ofsolar radiation and thesolar wind upon the

nucleus of the comet. Comet nuclei are themselves loose collections of ice, dust, and

small rocky particles, ranging from a few hundred meters to tens ofkilometers across.Comets have been observed since ancient times and have historically been considered

bad omens.

Comets have a wide range oforbital periods, ranging from a few years to hundreds ofthousands of years. Short-period comets originate in theKuiper Belt, or its associatedscattered disc,[1] which lie beyond the orbit ofNeptune. Longer-period comets are thought

to originate in the Oort Cloud, a cloud of icy bodies in the outer Solar System that were

left behind during the condensation of thesolar nebula. Long-period comets plungetowards the Sun from the Oort Cloud because ofgravitational perturbations caused by

either the massive outer planets of the Solar System (Jupiter,Saturn,Uranus, and
http://en.wikipedia.org/wiki/Comet_Hale-Bopphttp://en.wikipedia.org/wiki/Pazinhttp://en.wikipedia.org/wiki/Pazinhttp://en.wikipedia.org/wiki/Pazinhttp://en.wikipedia.org/wiki/Croatiahttp://en.wikipedia.org/wiki/Small_Solar_System_bodyhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Solar_radiationhttp://en.wikipedia.org/wiki/Solar_radiationhttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Comet_nucleushttp://en.wikipedia.org/wiki/P/2007_R5http://en.wikipedia.org/wiki/Kilometerhttp://en.wikipedia.org/wiki/Orbital_periodhttp://en.wikipedia.org/wiki/Orbital_periodhttp://en.wikipedia.org/wiki/Orbital_periodhttp://en.wikipedia.org/wiki/Kuiper_Belthttp://en.wikipedia.org/wiki/Kuiper_Belthttp://en.wikipedia.org/wiki/Scattered_dischttp://en.wikipedia.org/wiki/Comet#cite_note-Davidsson-0%23cite_note-Davidsson-0http://en.wikipedia.org/wiki/Neptunehttp://en.wikipedia.org/wiki/Oort_Cloudhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Solar_nebulahttp://en.wikipedia.org/wiki/Solar_nebulahttp://en.wikipedia.org/wiki/Gravitational_perturbationhttp://en.wikipedia.org/wiki/Gravitational_perturbationhttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Saturnhttp://en.wikipedia.org/wiki/Uranushttp://en.wikipedia.org/wiki/Uranushttp://en.wikipedia.org/wiki/Uranushttp://en.wikipedia.org/wiki/File:Comet-Hale-Bopp-29-03-1997_hires_adj.jpghttp://en.wikipedia.org/wiki/Comet_Hale-Bopphttp://en.wikipedia.org/wiki/Pazinhttp://en.wikipedia.org/wiki/Croatiahttp://en.wikipedia.org/wiki/Small_Solar_System_bodyhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Solar_radiationhttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Comet_nucleushttp://en.wikipedia.org/wiki/P/2007_R5http://en.wikipedia.org/wiki/Kilometerhttp://en.wikipedia.org/wiki/Orbital_periodhttp://en.wikipedia.org/wiki/Kuiper_Belthttp://en.wikipedia.org/wiki/Scattered_dischttp://en.wikipedia.org/wiki/Comet#cite_note-Davidsson-0%23cite_note-Davidsson-0http://en.wikipedia.org/wiki/Neptunehttp://en.wikipedia.org/wiki/Oort_Cloudhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Solar_nebulahttp://en.wikipedia.org/wiki/Gravitational_perturbationhttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Saturnhttp://en.wikipedia.org/wiki/Uranus


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Neptune), orpassing stars. Rare hyperbolic comets pass once through the inner SolarSystem before being thrown out into interstellar space along hyperbolic trajectories.

Comets are distinguished from asteroidsby the presence of a comaor atail. However,

extinct comets that have passed close to the Sun many times have lost nearly all of their

volatile ices and dust, and may come to resemble small asteroids. [2] Asteroids are thoughtto have a different origin from comets, having formed inside the orbit ofJupiterrather

than in the outer Solar System.[3][4]These have somewhat blurred the distinction between

asteroids and comets (see centaursand asteroid terminology).

As of May 2010 there are a reported 3,976 known comets[5] of which about 1,500 areKreutz Sungrazers and about 484 are short-period.[6] This number is steadily increasing.

However, this represents only a tiny fraction of the total potential comet population: the

reservoir of comet-like bodies in the outer solar system may number one trillion.[7] Thenumber visible to the naked eye averages roughly one per year, though many of these are

faint and unspectacular.[8] Particularly bright or notable examples are called "Great

Comets".

From Wikipedia, the free encyclopedia

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This article is about the astronomical object. For other uses, see Comet(disambiguation).

Comet Hale-Bopp, as seen on 29 March 1997 inPazin,Croatia.

A comet is an icy small Solar System body that, when close enough to the Sun, displays

a visible coma(a thin, fuzzy, temporary atmosphere), and sometimes also a tail. These

phenomena are both due to the effects ofsolar radiation and thesolar wind upon thenucleus of the comet. Comet nuclei are themselves loose collections of ice, dust, and

small rocky particles, ranging from a few hundred meters to tens ofkilometers across.Comets have been observed since ancient times and have historically been considered

bad omens.

Comets have a wide range oforbital periods, ranging from a few years to hundreds of

thousands of years. Short-period comets originate in theKuiper Belt, or its associated
http://en.wikipedia.org/wiki/Neptunehttp://en.wikipedia.org/wiki/List_of_nearest_starshttp://en.wikipedia.org/wiki/Hyperbolichttp://en.wikipedia.org/wiki/Inner_Solar_Systemhttp://en.wikipedia.org/wiki/Inner_Solar_Systemhttp://en.wikipedia.org/wiki/Interstellar_spacehttp://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Asteroidhttp://en.wikipedia.org/wiki/Asteroidhttp://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Extinct_cometshttp://en.wikipedia.org/wiki/Volatility_(chemistry)http://en.wikipedia.org/wiki/Comet#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Comet#cite_note-2%23cite_note-2http://en.wikipedia.org/wiki/Comet#cite_note-3%23cite_note-3http://en.wikipedia.org/wiki/Comet#cite_note-3%23cite_note-3http://en.wikipedia.org/wiki/Centaur_(minor_planet)http://en.wikipedia.org/wiki/Centaur_(minor_planet)http://en.wikipedia.org/wiki/Asteroid#Terminologyhttp://en.wikipedia.org/wiki/Comet#cite_note-4%23cite_note-4http://en.wikipedia.org/wiki/Kreutz_Sungrazershttp://en.wikipedia.org/wiki/Comet#cite_note-5%23cite_note-5http://en.wikipedia.org/wiki/Comet#cite_note-6%23cite_note-6http://en.wikipedia.org/wiki/Naked_eyehttp://en.wikipedia.org/wiki/Comet#cite_note-7%23cite_note-7http://en.wikipedia.org/wiki/Great_Comethttp://en.wikipedia.org/wiki/Great_Comethttp://en.wikipedia.org/wiki/Comet#mw-head%23mw-headhttp://en.wikipedia.org/wiki/Comet#mw-head%23mw-headhttp://en.wikipedia.org/wiki/Comet#p-search%23p-searchhttp://en.wikipedia.org/wiki/Comet_(disambiguation)http://en.wikipedia.org/wiki/Comet_(disambiguation)http://en.wikipedia.org/wiki/Comet_Hale-Bopphttp://en.wikipedia.org/wiki/Pazinhttp://en.wikipedia.org/wiki/Pazinhttp://en.wikipedia.org/wiki/Pazinhttp://en.wikipedia.org/wiki/Croatiahttp://en.wikipedia.org/wiki/Small_Solar_System_bodyhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Solar_radiationhttp://en.wikipedia.org/wiki/Solar_radiationhttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Comet_nucleushttp://en.wikipedia.org/wiki/P/2007_R5http://en.wikipedia.org/wiki/Kilometerhttp://en.wikipedia.org/wiki/Orbital_periodhttp://en.wikipedia.org/wiki/Orbital_periodhttp://en.wikipedia.org/wiki/Orbital_periodhttp://en.wikipedia.org/wiki/Kuiper_Belthttp://en.wikipedia.org/wiki/Kuiper_Belthttp://en.wikipedia.org/wiki/File:Comet-Hale-Bopp-29-03-1997_hires_adj.jpghttp://en.wikipedia.org/wiki/Neptunehttp://en.wikipedia.org/wiki/List_of_nearest_starshttp://en.wikipedia.org/wiki/Hyperbolichttp://en.wikipedia.org/wiki/Inner_Solar_Systemhttp://en.wikipedia.org/wiki/Inner_Solar_Systemhttp://en.wikipedia.org/wiki/Interstellar_spacehttp://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Asteroidhttp://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Extinct_cometshttp://en.wikipedia.org/wiki/Volatility_(chemistry)http://en.wikipedia.org/wiki/Comet#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Comet#cite_note-2%23cite_note-2http://en.wikipedia.org/wiki/Comet#cite_note-3%23cite_note-3http://en.wikipedia.org/wiki/Centaur_(minor_planet)http://en.wikipedia.org/wiki/Asteroid#Terminologyhttp://en.wikipedia.org/wiki/Comet#cite_note-4%23cite_note-4http://en.wikipedia.org/wiki/Kreutz_Sungrazershttp://en.wikipedia.org/wiki/Comet#cite_note-5%23cite_note-5http://en.wikipedia.org/wiki/Comet#cite_note-6%23cite_note-6http://en.wikipedia.org/wiki/Naked_eyehttp://en.wikipedia.org/wiki/Comet#cite_note-7%23cite_note-7http://en.wikipedia.org/wiki/Great_Comethttp://en.wikipedia.org/wiki/Great_Comethttp://en.wikipedia.org/wiki/Comet#mw-head%23mw-headhttp://en.wikipedia.org/wiki/Comet#p-search%23p-searchhttp://en.wikipedia.org/wiki/Comet_(disambiguation)http://en.wikipedia.org/wiki/Comet_(disambiguation)http://en.wikipedia.org/wiki/Comet_Hale-Bopphttp://en.wikipedia.org/wiki/Pazinhttp://en.wikipedia.org/wiki/Croatiahttp://en.wikipedia.org/wiki/Small_Solar_System_bodyhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Solar_radiationhttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Comet_nucleushttp://en.wikipedia.org/wiki/P/2007_R5http://en.wikipedia.org/wiki/Kilometerhttp://en.wikipedia.org/wiki/Orbital_periodhttp://en.wikipedia.org/wiki/Kuiper_Belt


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scattered disc,[1] which lie beyond the orbit ofNeptune. Longer-period comets are thoughtto originate in the Oort Cloud, a cloud of icy bodies in the outer Solar System that were

left behind during the condensation of thesolar nebula. Long-period comets plunge

towards the Sun from the Oort Cloud because ofgravitational perturbations caused byeither the massive outer planets of the Solar System (Jupiter,Saturn,Uranus, and

Neptune), orpassing stars. Rare hyperbolic comets pass once through the inner Solar

System before being thrown out into interstellar space along hyperbolic trajectories.

Comets are distinguished from asteroidsby the presence of a comaor atail. However,extinct comets that have passed close to the Sun many times have lost nearly all of their

volatile ices and dust, and may come to resemble small asteroids. [2] Asteroids are thought

to have a different origin from comets, having formed inside the orbit ofJupiterratherthan in the outer Solar System.[3][4]These have somewhat blurred the distinction between

asteroids and comets (see centaursand asteroid terminology).

As of May 2010 there are a reported 3,976 known comets[5] of which about 1,500 are

Kreutz Sungrazers and about 484 are short-period.[6] This number is steadily increasing.However, this represents only a tiny fraction of the total potential comet population: the

reservoir of comet-like bodies in the outer solar system may number one trillion.[7] The

number visible to the naked eye averages roughly one per year, though many of these are

faint and unspectacular.[8] Particularly bright or notable examples are called "GreatComets".
http://en.wikipedia.org/wiki/Scattered_dischttp://en.wikipedia.org/wiki/Comet#cite_note-Davidsson-0%23cite_note-Davidsson-0http://en.wikipedia.org/wiki/Neptunehttp://en.wikipedia.org/wiki/Oort_Cloudhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Solar_nebulahttp://en.wikipedia.org/wiki/Solar_nebulahttp://en.wikipedia.org/wiki/Gravitational_perturbationhttp://en.wikipedia.org/wiki/Gravitational_perturbationhttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Saturnhttp://en.wikipedia.org/wiki/Uranushttp://en.wikipedia.org/wiki/Uranushttp://en.wikipedia.org/wiki/Uranushttp://en.wikipedia.org/wiki/Neptunehttp://en.wikipedia.org/wiki/List_of_nearest_starshttp://en.wikipedia.org/wiki/Hyperbolichttp://en.wikipedia.org/wiki/Inner_Solar_Systemhttp://en.wikipedia.org/wiki/Inner_Solar_Systemhttp://en.wikipedia.org/wiki/Interstellar_spacehttp://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Asteroidhttp://en.wikipedia.org/wiki/Asteroidhttp://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Extinct_cometshttp://en.wikipedia.org/wiki/Volatility_(chemistry)http://en.wikipedia.org/wiki/Comet#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Comet#cite_note-2%23cite_note-2http://en.wikipedia.org/wiki/Comet#cite_note-3%23cite_note-3http://en.wikipedia.org/wiki/Comet#cite_note-3%23cite_note-3http://en.wikipedia.org/wiki/Centaur_(minor_planet)http://en.wikipedia.org/wiki/Centaur_(minor_planet)http://en.wikipedia.org/wiki/Asteroid#Terminologyhttp://en.wikipedia.org/wiki/Comet#cite_note-4%23cite_note-4http://en.wikipedia.org/wiki/Kreutz_Sungrazershttp://en.wikipedia.org/wiki/Comet#cite_note-5%23cite_note-5http://en.wikipedia.org/wiki/Comet#cite_note-6%23cite_note-6http://en.wikipedia.org/wiki/Naked_eyehttp://en.wikipedia.org/wiki/Comet#cite_note-7%23cite_note-7http://en.wikipedia.org/wiki/Great_Comethttp://en.wikipedia.org/wiki/Great_Comethttp://en.wikipedia.org/wiki/Scattered_dischttp://en.wikipedia.org/wiki/Comet#cite_note-Davidsson-0%23cite_note-Davidsson-0http://en.wikipedia.org/wiki/Neptunehttp://en.wikipedia.org/wiki/Oort_Cloudhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Solar_nebulahttp://en.wikipedia.org/wiki/Gravitational_perturbationhttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Saturnhttp://en.wikipedia.org/wiki/Uranushttp://en.wikipedia.org/wiki/Neptunehttp://en.wikipedia.org/wiki/List_of_nearest_starshttp://en.wikipedia.org/wiki/Hyperbolichttp://en.wikipedia.org/wiki/Inner_Solar_Systemhttp://en.wikipedia.org/wiki/Inner_Solar_Systemhttp://en.wikipedia.org/wiki/Interstellar_spacehttp://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Asteroidhttp://en.wikipedia.org/wiki/Coma_(cometary)http://en.wikipedia.org/wiki/Comet_tailhttp://en.wikipedia.org/wiki/Extinct_cometshttp://en.wikipedia.org/wiki/Volatility_(chemistry)http://en.wikipedia.org/wiki/Comet#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Comet#cite_note-2%23cite_note-2http://en.wikipedia.org/wiki/Comet#cite_note-3%23cite_note-3http://en.wikipedia.org/wiki/Centaur_(minor_planet)http://en.wikipedia.org/wiki/Asteroid#Terminologyhttp://en.wikipedia.org/wiki/Comet#cite_note-4%23cite_note-4http://en.wikipedia.org/wiki/Kreutz_Sungrazershttp://en.wikipedia.org/wiki/Comet#cite_note-5%23cite_note-5http://en.wikipedia.org/wiki/Comet#cite_note-6%23cite_note-6http://en.wikipedia.org/wiki/Naked_eyehttp://en.wikipedia.org/wiki/Comet#cite_note-7%23cite_note-7http://en.wikipedia.org/wiki/Great_Comethttp://en.wikipedia.org/wiki/Great_Comet


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Contents

[hide]

1 Etymology

2 Physical characteristics

o 2.1 Nucleus

o 2.2 Coma and tail

o 2.3 Connection to meteor showers

3 Orbital characteristics

4 Fate of cometso 4.1 Departure/ejection from Solar System

o 4.2 Volatiles exhausted

o 4.3 Breakup/disintegration

o 4.4 Collisions

5 Nomenclature

6 History of studyo 6.1 Early observations and thought

o 6.2 Orbital studies

o 6.3 Studies of physical characteristics

6.3.1 Recent findings

7 Notable cometso 7.1 Great comets

o 7.2 Sungrazing comets

o 7.3 Unusual comets

8 Observation 9 In popular culture

10 See also

11 References

12 Further reading

13 External links

[edit] Etymology

The word cometcame to English by way of theLatin word cometes. This word, in turn,

came from the Greekword , which means "hair of the head". TheGreekscientist

and philosopherAristotle first used the derived form of, , to describe what

he saw as "stars with hair." Theastronomical symbol for comets is (), consisting of asmall disc with three hairlike extensions.

[edit] Physical characteristics

[edit] Nucleus
http://en.wikipedia.org/wiki/Comet#%23http://en.wikipedia.org/wiki/Comet#Etymology%23Etymologyhttp://en.wikipedia.org/wiki/Comet#Physical_characteristics%23Physical_characteristicshttp://en.wikipedia.org/wiki/Comet#Nucleus%23Nucleushttp://en.wikipedia.org/wiki/Comet#Coma_and_tail%23Coma_and_tailhttp://en.wikipedia.org/wiki/Comet#Connection_to_meteor_showers%23Connection_to_meteor_showershttp://en.wikipedia.org/wiki/Comet#Orbital_characteristics%23Orbital_characteristicshttp://en.wikipedia.org/wiki/Comet#Fate_of_comets%23Fate_of_cometshttp://en.wikipedia.org/wiki/Comet#Departure.2Fejection_from_Solar_System%23Departure.2Fejection_from_Solar_Systemhttp://en.wikipedia.org/wiki/Comet#Volatiles_exhausted%23Volatiles_exhaustedhttp://en.wikipedia.org/wiki/Comet#Breakup.2Fdisintegration%23Breakup.2Fdisintegrationhttp://en.wikipedia.org/wiki/Comet#Collisions%23Collisionshttp://en.wikipedia.org/wiki/Comet#Nomenclature%23Nomenclaturehttp://en.wikipedia.org/wiki/Comet#History_of_study%23History_of_studyhttp://en.wikipedia.org/wiki/Comet#Early_observations_and_thought%23Early_observations_and_thoughthttp://en.wikipedia.org/wiki/Comet#Orbital_studies%23Orbital_studieshttp://en.wikipedia.org/wiki/Comet#Studies_of_physical_characteristics%23Studies_of_physical_characteristicshttp://en.wikipedia.org/wiki/Comet#Recent_findings%23Recent_findingshttp://en.wikipedia.org/wiki/Comet#Notable_comets%23Notable_cometshttp://en.wikipedia.org/wiki/Comet#Great_comets%23Great_cometshttp://en.wikipedia.org/wiki/Comet#Sungrazing_comets%23Sungrazing_cometshttp://en.wikipedia.org/wiki/Comet#Unusual_comets%23Unusual_cometshttp://en.wikipedia.org/wiki/Comet#Observation%23Observationhttp://en.wikipedia.org/wiki/Comet#In_popular_culture%23In_popular_culturehttp://en.wikipedia.org/wiki/Comet#See_also%23See_alsohttp://en.wikipedia.org/wiki/Comet#References%23Referenceshttp://en.wikipedia.org/wiki/Comet#Further_reading%23Further_readinghttp://en.wikipedia.org/wiki/Comet#External_links%23External_linkshttp://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=1http://en.wikipedia.org/wiki/English_languagehttp://en.wikipedia.org/wiki/Latinhttp://en.wikipedia.org/wiki/Latinhttp://en.wikipedia.org/wiki/Greek_Languagehttp://en.wikipedia.org/wiki/Greekshttp://en.wikipedia.org/wiki/Greekshttp://en.wikipedia.org/wiki/Aristotlehttp://en.wikipedia.org/wiki/Astronomical_symbolhttp://en.wikipedia.org/wiki/Astronomical_symbolhttp://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=2http://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=3http://en.wikipedia.org/wiki/Comet#%23http://en.wikipedia.org/wiki/Comet#Etymology%23Etymologyhttp://en.wikipedia.org/wiki/Comet#Physical_characteristics%23Physical_characteristicshttp://en.wikipedia.org/wiki/Comet#Nucleus%23Nucleushttp://en.wikipedia.org/wiki/Comet#Coma_and_tail%23Coma_and_tailhttp://en.wikipedia.org/wiki/Comet#Connection_to_meteor_showers%23Connection_to_meteor_showershttp://en.wikipedia.org/wiki/Comet#Orbital_characteristics%23Orbital_characteristicshttp://en.wikipedia.org/wiki/Comet#Fate_of_comets%23Fate_of_cometshttp://en.wikipedia.org/wiki/Comet#Departure.2Fejection_from_Solar_System%23Departure.2Fejection_from_Solar_Systemhttp://en.wikipedia.org/wiki/Comet#Volatiles_exhausted%23Volatiles_exhaustedhttp://en.wikipedia.org/wiki/Comet#Breakup.2Fdisintegration%23Breakup.2Fdisintegrationhttp://en.wikipedia.org/wiki/Comet#Collisions%23Collisionshttp://en.wikipedia.org/wiki/Comet#Nomenclature%23Nomenclaturehttp://en.wikipedia.org/wiki/Comet#History_of_study%23History_of_studyhttp://en.wikipedia.org/wiki/Comet#Early_observations_and_thought%23Early_observations_and_thoughthttp://en.wikipedia.org/wiki/Comet#Orbital_studies%23Orbital_studieshttp://en.wikipedia.org/wiki/Comet#Studies_of_physical_characteristics%23Studies_of_physical_characteristicshttp://en.wikipedia.org/wiki/Comet#Recent_findings%23Recent_findingshttp://en.wikipedia.org/wiki/Comet#Notable_comets%23Notable_cometshttp://en.wikipedia.org/wiki/Comet#Great_comets%23Great_cometshttp://en.wikipedia.org/wiki/Comet#Sungrazing_comets%23Sungrazing_cometshttp://en.wikipedia.org/wiki/Comet#Unusual_comets%23Unusual_cometshttp://en.wikipedia.org/wiki/Comet#Observation%23Observationhttp://en.wikipedia.org/wiki/Comet#In_popular_culture%23In_popular_culturehttp://en.wikipedia.org/wiki/Comet#See_also%23See_alsohttp://en.wikipedia.org/wiki/Comet#References%23Referenceshttp://en.wikipedia.org/wiki/Comet#Further_reading%23Further_readinghttp://en.wikipedia.org/wiki/Comet#External_links%23External_linkshttp://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=1http://en.wikipedia.org/wiki/English_languagehttp://en.wikipedia.org/wiki/Latinhttp://en.wikipedia.org/wiki/Greek_Languagehttp://en.wikipedia.org/wiki/Greekshttp://en.wikipedia.org/wiki/Aristotlehttp://en.wikipedia.org/wiki/Astronomical_symbolhttp://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=2http://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=3


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Nucleus of comet Tempel 1imaged by the Deep Impact impactor. The nucleus measures

about 6 kilometres across.

Comet Holmes (17P/Holmes) in 2007 showing blue ion tail on right

Main article: Comet nucleus

Comet nuclei are known to range from about 100 meters to more than 40 kilometresacross. They are composed ofrock,dust,water ice, and frozen gases such as carbon

monoxide, carbon dioxide, methaneand ammonia.[9] Because of their low mass, comet

nuclei do notbecome sphericalunder their own gravity, and thus have irregular shapes.

They are often popularly described as "dirty snowballs", though recent observations have

revealed dry dusty or rocky surfaces, suggesting that the ices are hidden beneath thecrust. Comets also contain a variety oforganic compounds; in addition to the gases

already mentioned, these may includemethanol,hydrogen cyanide, formaldehyde,ethanoland ethane, and perhaps more complex molecules such as long-chain

hydrocarbonsand amino acids.[10][11][12] In 2009, it was confirmed that the amino acid

glycinehad been found in the comet dust recovered by NASA'sStardust mission.[13]

Surprisingly, cometary nuclei are among the least reflective objects found in our solarsystem. The Giottospace probe found that the nucleus ofHalley's Comet reflects about

four percent of the light that falls on it,[14] and Deep Space 1discovered that Comet

Borrelly's surface reflects just 2.4% to 3.0% of the light that falls on it;[14] by comparison,

asphalt reflects seven percent of the light that falls on it. It is thought that complexorganic compounds are the dark surface material. Solar heating drives off volatile

compounds leaving behind heavy long-chain organics[clarification needed] that tend to be very

dark, like tarorcrude oil. The very darkness of cometary surfaces enables them to absorbthe heat necessary to drive their outgassing processes.

[edit] Coma and tail
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Main articles: Coma (cometary) and Comet tail

In the outer solar system, comets remain frozen and are extremely difficult or impossibleto detect from Earth due to their small size. Statistical detections of inactive comet nuclei

in the Kuiper belthave been reported from theHubble Space Telescopeobservations,[15]

[16] but these detections have been questioned,[17][18] and have not yet been independentlyconfirmed. As a comet approaches the inner solar system,solar radiationcauses the

volatile materials within the comet to vaporize and stream out of the nucleus, carrying

dust away with them. The streams ofdust and gas thus released form a huge, extremelytenuous atmosphere around the comet called the coma, and the force exerted on the coma

by the Sun's radiation pressure and solar wind cause an enormous tailto form, which

points away from the sun.

Both the coma and tail are illuminated by the Sun and may become visible from Earthwhen a comet passes through the inner solar system, the dust reflecting sunlight directly

and the gases glowing from ionisation. Most comets are too faint to be visible without the

aid of a telescope, but a few each decade become bright enough to be visible to the nakedeye. Occasionally a comet may experience a huge and sudden outburst of gas and dust,

during which the size of the coma temporarily greatly increases in size. This happened in

2007 to Comet Holmes.[citation needed]

The streams of dust and gas each form their own distinct tail, pointing in slightly differentdirections. The tail of dust is left behind in the comet's orbit in such a manner that it often

forms a curved[citation needed] tail called the type II or dust tail. At the same time, the ion or

type I tail, made of gases, always points directly away from the Sun, as this gas is morestrongly affected by the solar wind than is dust, following magnetic field lines rather than

an orbital trajectory. On occasions a short tail pointing in the opposite direction to the ion

and dust tails may be seen the antitail. These were once thought to be somewhat

mysterious, but are merely the end of the dust tail apparently projecting ahead of thecomet due to our viewing angle.[19]

While the solid nucleus of comets is generally less than 50 km (31 mi) across, the coma

may be larger than the Sun, and ion tails have been observed to extend one astronomical

unit (150 million km) or more.[9] The observation of antitails contributed significantly tothe discovery ofsolar wind.[20]The ion tail is formed as a result of thephotoelectric

effect[dubiousdiscuss] of solar ultra-violet radiation acting on particles in the coma. Once the

particles have been ionized, they attain a net positive electrical charge which in turn givesrise to an "induced magnetosphere" around the comet. The comet and its induced

magnetic field form an obstacle to outward flowing solar wind particles. As the relative

orbital speed of the comet and the solar wind is supersonic, abow shockis formedupstream of the comet, in the flow direction of the solar wind. In this bow shock, large

concentrations of cometary ions (called "pick-up ions") congregate and act to "load" the

solar magnetic field with plasma, such that the field lines "drape" around the cometforming the ion tail.[21]
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Encke's Comet loses its tail

If the ion tail loading is sufficient, then the magnetic field lines are squeezed together to

the point where, at some distance along the ion tail, magnetic reconnection occurs. This

leads to a "tail disconnection event".[21] This has been observed on a number of occasions,one notable event recorded on April 20, 2007, when the ion tail ofEncke's Comet was

completely severed while the comet passed through a coronal mass ejection. This event

was observed by the STEREO space probe.[22]

Comets were found to emit X-raysin 1996.[23]This surprised researchers, because X-rayemission is usually associated with very high-temperature bodies. The X-rays are thought

to be generated by the interaction between comets and the solar wind: when highly

charged ions fly through a cometary atmosphere, they collide with cometary atoms andmolecules, "ripping off" one or more electrons from the comet. This ripping off leads to

the emission of X-rays and far ultravioletphotons.[24]

[edit] Connection to meteor showers

As a result of outgassing, comets leave a trail of solid debris. If the comet's path crosses

Earth's path, then at that point there will likely be meteor showers as Earth passes through

the trail of debris. The Perseid meteor showeroccurs every year between August 9 andAugust 13, when Earth passes through the orbit of theSwiftTuttle comet.[25]Halley's

cometis the source of the Orionid showerin October.[25]

[edit] Orbital characteristics

Orbits of the Kohoutek Comet (red) and the Earth(blue), illustrating the high eccentricity

of its orbit and its rapid motion when close to the Sun.

Histogram of the aphelia of the 2005 comets, showing the giant planet comet families.The abscissa is thenatural logarithm of the aphelion expressed in AUs.

Most comets have elongated elliptical orbitsthat take them close to the Sun for a part of

their orbit, and then out into the further reaches of the Solar System for the remainder.

Comets are often classified according to the length of theirorbital periods: the longer theperiod the more elongated the ellipse.

Short-period comets are generally defined as having orbital periods of less than

200 years. They usually orbit more-or-less in the eclipticplane in the same

direction as the planets. Their orbits typically take them out to the region of the

outer planets (Jupiter and beyond) ataphelion; for example, the aphelion ofHalley's Comet is a little beyond the orbit ofNeptune. At the shorter extreme,

Encke's Comet has an orbit which never puts it farther away from the Sun thanJupiter. Short-period comets are further divided into the Jupiter family (periods

less than 20 years) and Halley family (periods between 20 and 200 years).

Long-period comets have highly eccentric orbits and periods ranging from 200years to thousands or even millions of years. (However, by definition they remain

gravitationally bound to the Sun; those comets that are ejected from the solar
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system due to close passes by major planets are no longer properly considered ashaving "periods".) Their orbits take them far beyond the outer planets at aphelia,

and the plane of their orbits need not lie near the ecliptic.

Single-apparition comets are similar to long-period comets, but haveparabolicor slightly hyperbolictrajectories[26]when in the inner Solar System. However,

gravitational perturbations from giant planets cause their orbits to change, and

when in the outer Solar System their orbits are highly eccentricand elliptical with

aphelia lying beyond the Oort Cloud. (See C/2007 N3 (Lulin) as an example.)[citation needed] The Sun'shill sphere has an unstable maximum boundary of

230,000 AU (1.1 parsecs (3.6 light-years)).[27] All comets with parabolic and

slightly hyperbolic orbits belong to the Solar System and had certain orbitalperiods, generally hundreds of thousand, or millions of years before being

perturbed onto an ejection trajectory.[citation needed][contradiction] Only a few hundred

comets have been seen to achieve a genuine hyperbolic orbit[citation needed] that usingcelestial mechanics suggests they will escape the Solar System. No comets with

aneccentricitysignificantly greater than one have been observed,[citation needed] so

there are no confirmed observations of comets that likely did not originate in theSolar System. As of a 2010Epoch, Comet C/1980 E1 has the largest eccentricity

of any known hyperboliccomet with an eccentricity of 1.057.[28]

Some authorities use the term periodic comet to refer to any comet with a

periodic orbit (that is, all short-period comets plus all long-period comets),[29]

while others use it to mean exclusively short-period comets.[26] Similarly, although

the literal meaning ofnon-periodic comet is the same as "single-apparition

comet", some use it to mean all comets that are not "periodic" in the second sense

(that is, to also include all comets with a period greater than 200 years). Recently discoveredmain-belt cometsform a distinct class, orbiting in more

circular orbits within the asteroid belt.[30][31]

Based on their orbital characteristics, short-period comets are thought to originate fromthe centaurs and the Kuiper belt/scattered disk[1] a disk of objects in the transneptunian

regionwhereas the source of long-period comets is thought to be the far more distant

spherical Oort cloud (after the Dutch astronomerJan Hendrik Oortwho hypothesised its

existence).[32]Vast swarms of comet-like bodies are believed to orbit the Sun in thesedistant regions in roughly circular orbits. Occasionally the gravitational influence of the

outer planets (in the case of Kuiper Belt objects) or nearby stars (in the case of Oort cloud

objects) may throw one of these bodies into an elliptical orbit that takes it inwardstowards the Sun, to form a visible comet. Unlike the return of periodic comets whose

orbits have been established by previous observations, the appearance of new comets by

this mechanism is unpredictable.

Since their elliptical orbits frequently take them close to the giant planets, comets aresubject to further gravitational perturbations. Short period comets display a tendency for

theiraphelia to coincide with a giant planet's orbital radius, with the Jupiter family of

comets being the largest, as the histogram shows. It is clear that comets coming in fromthe Oort cloud often have their orbits strongly influenced by the gravity of giant planets

as a result of a close encounter. Jupiter is the source of the greatest perturbations, being

more than twice as massive as all the other planets combined, in addition to being theswiftest of the giant planets. These perturbations probably sometimes deflect long-period

comets into shorter orbital periods, with Halley's Comet being a possible example of this.
http://en.wikipedia.org/wiki/Parabolic_trajectoryhttp://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Comet#cite_note-SBP-25%23cite_note-SBP-25http://en.wikipedia.org/wiki/Comet#cite_note-SBP-25%23cite_note-SBP-25http://en.wikipedia.org/wiki/Orbital_eccentricityhttp://en.wikipedia.org/wiki/Orbital_eccentricityhttp://en.wikipedia.org/wiki/Oort_Cloudhttp://en.wikipedia.org/wiki/Comet_Lulinhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Hill_spherehttp://en.wikipedia.org/wiki/Hill_spherehttp://en.wikipedia.org/wiki/Comet#cite_note-Chebotarev1964-26%23cite_note-Chebotarev1964-26http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Cleanuphttp://en.wikipedia.org/wiki/Wikipedia:Cleanuphttp://en.wikipedia.org/wiki/Wikipedia:Cleanuphttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Celestial_mechanicshttp://en.wikipedia.org/wiki/Eccentricity_(mathematics)http://en.wikipedia.org/wiki/Eccentricity_(mathematics)http://en.wikipedia.org/wiki/Eccentricity_(mathematics)http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Epoch_(astronomy)http://en.wikipedia.org/wiki/Epoch_(astronomy)http://en.wikipedia.org/wiki/C/1980_E1http://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Comet#cite_note-C.2F1980E1-jpl-27%23cite_note-C.2F1980E1-jpl-27http://en.wikipedia.org/wiki/Comet#cite_note-28%23cite_note-28http://en.wikipedia.org/wiki/Comet#cite_note-28%23cite_note-28http://en.wikipedia.org/wiki/Comet#cite_note-SBP-25%23cite_note-SBP-25http://en.wikipedia.org/wiki/Main-belt_cometshttp://en.wikipedia.org/wiki/Main-belt_cometshttp://en.wikipedia.org/wiki/Main-belt_cometshttp://en.wikipedia.org/wiki/Asteroid_belthttp://en.wikipedia.org/wiki/Asteroid_belthttp://en.wikipedia.org/wiki/Comet#cite_note-29%23cite_note-29http://en.wikipedia.org/wiki/Comet#cite_note-30%23cite_note-30http://en.wikipedia.org/wiki/Centaur_(minor_planet)http://en.wikipedia.org/wiki/Kuiper_belthttp://en.wikipedia.org/wiki/Scattered_diskhttp://en.wikipedia.org/wiki/Comet#cite_note-Davidsson-0%23cite_note-Davidsson-0http://en.wikipedia.org/wiki/Comet#cite_note-Davidsson-0%23cite_note-Davidsson-0http://en.wikipedia.org/wiki/Oort_cloudhttp://en.wikipedia.org/wiki/Jan_Hendrik_Oorthttp://en.wikipedia.org/wiki/Jan_Hendrik_Oorthttp://en.wikipedia.org/wiki/Comet#cite_note-31%23cite_note-31http://en.wikipedia.org/wiki/Comet#cite_note-31%23cite_note-31http://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Apsishttp://en.wikipedia.org/wiki/Giant_planethttp://en.wikipedia.org/wiki/Giant_planethttp://en.wikipedia.org/wiki/Histogramhttp://en.wikipedia.org/wiki/Parabolic_trajectoryhttp://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Comet#cite_note-SBP-25%23cite_note-SBP-25http://en.wikipedia.org/wiki/Orbital_eccentricityhttp://en.wikipedia.org/wiki/Oort_Cloudhttp://en.wikipedia.org/wiki/Comet_Lulinhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Hill_spherehttp://en.wikipedia.org/wiki/Comet#cite_note-Chebotarev1964-26%23cite_note-Chebotarev1964-26http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Cleanuphttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Celestial_mechanicshttp://en.wikipedia.org/wiki/Eccentricity_(mathematics)http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Epoch_(astronomy)http://en.wikipedia.org/wiki/C/1980_E1http://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Comet#cite_note-C.2F1980E1-jpl-27%23cite_note-C.2F1980E1-jpl-27http://en.wikipedia.org/wiki/Comet#cite_note-28%23cite_note-28http://en.wikipedia.org/wiki/Comet#cite_note-SBP-25%23cite_note-SBP-25http://en.wikipedia.org/wiki/Main-belt_cometshttp://en.wikipedia.org/wiki/Asteroid_belthttp://en.wikipedia.org/wiki/Comet#cite_note-29%23cite_note-29http://en.wikipedia.org/wiki/Comet#cite_note-30%23cite_note-30http://en.wikipedia.org/wiki/Centaur_(minor_planet)http://en.wikipedia.org/wiki/Kuiper_belthttp://en.wikipedia.org/wiki/Scattered_diskhttp://en.wikipedia.org/wiki/Comet#cite_note-Davidsson-0%23cite_note-Davidsson-0http://en.wikipedia.org/wiki/Oort_cloudhttp://en.wikipedia.org/wiki/Jan_Hendrik_Oorthttp://en.wikipedia.org/wiki/Comet#cite_note-31%23cite_note-31http://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Apsishttp://en.wikipedia.org/wiki/Giant_planethttp://en.wikipedia.org/wiki/Histogram


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Early observations have revealed a few genuinely hyperbolic (i.e. non-periodic)trajectories, but no more than could be accounted for by perturbations from Jupiter. If

comets pervaded interstellar space, they would be moving with velocities of the same

order as the relative velocities of stars near the Sun (a few tens of kilometres per second).If such objects entered the solar system, they would have positive total energies, and

would be observed to have genuinely hyperbolic trajectories. A rough calculation shows

that there might be four hyperbolic comets per century, [33] within Jupiter's orbit, give or

take one and perhaps two orders of magnitude.[citation needed]

A number of periodic comets discovered in earlier decades or previous centuries are now

"lost." Their orbits were never known well enough to predict future appearances.

However, occasionally a "new" comet will be discovered and upon calculation of its orbitit turns out to be an old "lost" comet. An example is Comet 11P/Tempel-Swift-LINEAR,

discovered in 1869 but unobservable after 1908 because of perturbations by Jupiter. It

was not found again until accidentally rediscovered by LINEARin 2001.[34]

[edit] Fate of comets

[edit] Departure/ejection from Solar System

If a comet is traveling fast enough, it may leave the Solar System; such is the case for

Hyperbolic comets. To date, comets are only known to be ejected by interacting withanother object in the solar system (see Perturbation), such asJupiter.

Material coming off Component B of73P/Schwassmann-Wachmannwhich broke upstarting in 1995, as seen by the HST. This animation covers a span of three days.

[edit] Volatiles exhausted

Main article: Extinct comet

Jupiter family comets (JFC) and long period comets (LPC) (see "Orbital characteristics",

above) appear to follow very different fading laws. The JFCs are active over a lifetime of

about 10,000 years or ~1,000 revolutions while the LPCs disappear much faster. Only10% of the LPCs survive more than 50 passages to small perihelion, while only 1% of

them survive more than 2,000 passages.[35]Eventually most of the volatile material

contained in a comet nucleus evaporates away, and the comet becomes a small, dark,

inert lump of rock or rubble that can resemble an asteroid.[36]
http://en.wikipedia.org/wiki/Comet#cite_note-32%23cite_note-32http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/11P/Tempel-Swift-LINEARhttp://en.wikipedia.org/wiki/LINEARhttp://en.wikipedia.org/wiki/LINEARhttp://en.wikipedia.org/wiki/Comet#cite_note-kronk-33%23cite_note-kronk-33http://en.wikipedia.org/wiki/Comet#cite_note-kronk-33%23cite_note-kronk-33http://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=8http://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Perturbation_(astronomy)http://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/73P/Schwassmann-Wachmannhttp://en.wikipedia.org/wiki/73P/Schwassmann-Wachmannhttp://en.wikipedia.org/wiki/Hubble_Space_Telescopehttp://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=9http://en.wikipedia.org/wiki/Extinct_comethttp://en.wikipedia.org/wiki/Comet#cite_note-dormant-34%23cite_note-dormant-34http://en.wikipedia.org/wiki/Comet#cite_note-dormant-34%23cite_note-dormant-34http://en.wikipedia.org/wiki/Comet#cite_note-dormant-34%23cite_note-dormant-34http://en.wikipedia.org/wiki/Asteroidhttp://en.wikipedia.org/wiki/Comet#cite_note-35%23cite_note-35http://en.wikipedia.org/wiki/File:Schwassman-Wachmann3-B-HST.gifhttp://en.wikipedia.org/wiki/Comet#cite_note-32%23cite_note-32http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/11P/Tempel-Swift-LINEARhttp://en.wikipedia.org/wiki/LINEARhttp://en.wikipedia.org/wiki/Comet#cite_note-kronk-33%23cite_note-kronk-33http://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=8http://en.wikipedia.org/wiki/Hyperbolic_trajectoryhttp://en.wikipedia.org/wiki/Perturbation_(astronomy)http://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/73P/Schwassmann-Wachmannhttp://en.wikipedia.org/wiki/Hubble_Space_Telescopehttp://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=9http://en.wikipedia.org/wiki/Extinct_comethttp://en.wikipedia.org/wiki/Comet#cite_note-dormant-34%23cite_note-dormant-34http://en.wikipedia.org/wiki/Asteroidhttp://en.wikipedia.org/wiki/Comet#cite_note-35%23cite_note-35


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[edit] Breakup/disintegration

Comets are also known to break up into fragments, as happened with Comet73P/Schwassmann-Wachmann 3 starting in 1995.[37]

This breakup may be triggered by tidal gravitational forces from the Sun or a large planet,

by an "explosion" of volatile material, or for other reasons not fully explained.

[edit] Collisions

Brown spots mark impact sites of the Shoemaker-Levy Cometon Jupiter's southernhemisphere.

Some comets meet a more spectacular endeither falling into the Sun,[38]or smashing

into a planet or other body. Collisions between comets and planets or moons were

common in the early Solar System: some of the many craters on the Earth's Moon, forexample, may have been caused by comets. A recent collision of a comet with a planet

occurred in July 1994 when Comet Shoemaker-Levy 9 broke up into pieces and collided

with Jupiter.

Many comets and asteroids collided into Earth in its early stages. Many scientists believethat comets bombarding the young Earth (about 4 billion years ago) brought the vast

quantities of water that now fill the Earth's oceans, or at least a significant proportion of

it. Other researchers have cast doubt on this theory.[39]The detection of organic moleculesin comets has led some to speculate that comets ormeteoritesmay have brought the

precursors of lifeor even life itselfto Earth.[11] There are still many near-Earth

comets, although a collision with an asteroid is more likely than with a comet.

It is suspected that comet impacts have, over long timescales, also delivered significantquantities of water to the Earth's Moon, some of which may have survived as lunar ice.

Comet and meteoroid impacts are believed to be responsible for the existence oftektitesandaustralites.

[edit] Nomenclature

The names given to comets have followed several different conventions over the past two

centuries. Before any systematic naming convention was adopted, comets were named in

a variety of ways. Prior to the early 20th century, most comets were simply referred to by
http://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=10http://en.wikipedia.org/wiki/73P/Schwassmann-Wachmannhttp://en.wikipedia.org/wiki/73P/Schwassmann-Wachmannhttp://en.wikipedia.org/wiki/Comet#cite_note-spitzer2006-36%23cite_note-spitzer2006-36http://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=11http://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9http://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9http://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Comet#cite_note-37%23cite_note-37http://en.wikipedia.org/wiki/Comet#cite_note-37%23cite_note-37http://en.wikipedia.org/wiki/Comet#cite_note-37%23cite_note-37http://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9http://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Comet#cite_note-38%23cite_note-38http://en.wikipedia.org/wiki/Comet#cite_note-38%23cite_note-38http://en.wikipedia.org/wiki/Comet#cite_note-38%23cite_note-38http://en.wikipedia.org/wiki/Meteoritehttp://en.wikipedia.org/wiki/Meteoritehttp://en.wikipedia.org/wiki/Comet#cite_note-cnnlife-10%23cite_note-cnnlife-10http://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Lunar_icehttp://en.wikipedia.org/wiki/Meteoroidhttp://en.wikipedia.org/wiki/Tektitehttp://en.wikipedia.org/wiki/Australitehttp://en.wikipedia.org/wiki/Australitehttp://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=12http://en.wikipedia.org/wiki/File:Jupiter_showing_SL9_impact_sites.jpghttp://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=10http://en.wikipedia.org/wiki/73P/Schwassmann-Wachmannhttp://en.wikipedia.org/wiki/73P/Schwassmann-Wachmannhttp://en.wikipedia.org/wiki/Comet#cite_note-spitzer2006-36%23cite_note-spitzer2006-36http://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=11http://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9http://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Comet#cite_note-37%23cite_note-37http://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9http://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Comet#cite_note-38%23cite_note-38http://en.wikipedia.org/wiki/Meteoritehttp://en.wikipedia.org/wiki/Comet#cite_note-cnnlife-10%23cite_note-cnnlife-10http://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Lunar_icehttp://en.wikipedia.org/wiki/Meteoroidhttp://en.wikipedia.org/wiki/Tektitehttp://en.wikipedia.org/wiki/Australitehttp://en.wikipedia.org/w/index.php?title=Comet&action=edit&section=12


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the year in which they appeared, sometimes with additional adjectives for particularlybright comets; thus, the "Great Comet of 1680" (Kirch's Comet), the "Great September

Comet of 1882", and the "Daylight Comet of 1910" ("Great January Comet of 1910").

Halley's Comet, named after the astronomerEdmund Halley for successfully calculating

its orbit

AfterEdmund Halley demonstrated that the comets of 1531, 1607, and 1682 were thesame body and successfully predicted its return in 1759, that comet became known as

Halley's Comet.[40] Similarly, the second and third known periodic comets, Encke's

Comet[41] and Biela's Comet,[42] were named after the astronomers who calculated theirorbits rather than their original discoverers. Later, periodic comets were usually named

after their discoverers, but comets that had appeared only once continued to be referred to

by the year of their apparition.

In the early 20th century, the convention of naming comets after their discoverers becamecommon, and this remains so today. A comet is named after up to three independent

discoverers. In recent years, many comets have been discovered by instruments operated

by large teams of astronomers, and in this case, comets may be named for the instrument.For example, Comet IRAS-Araki-Alcockwas discovered independently by the IRAS

satellite and amateur astronomers Genichi ArakiandGeorge Alcock. In the past, when

multiple comets were discovered by the same individual, group of individuals, or team,

the comets' names were distinguished by adding a numeral to the discoverers' names (butonly for periodic comets); thus Comets Shoemaker-Levy 19. Today, the large numbers

of comets discovered by some instruments has caused this system to be impractical, andno attempt is made to ensure that each comet is given a unique name. Instead, the comets'systematic designations are used to avoid confusion.

Until 1994, comets were first given aprovisional designation consisting of the year of

their discovery followed by a lowercase letter indicating its order of discovery in that

year (for example, Comet 1969i (Bennett) was the 9th comet discovered in 1969). Oncethe comet had been observed through perihelion and its orbit had been established, the

comet was given a permanent designation of the year of itsperihelion, followed by a

Roman numeral indicating its order of perihelion passage in that year, so that Comet1969i became Comet 1970 II (it was the second comet to pass perihelion in 1970)[43]

Increasing numbers of comet discoveries made this procedure awkward, and in 1994 the

International Astronomical Union approved a new naming system. Comets are now

designated by the year of their discovery followed by a letter indicating the half-month ofthe discovery and a number indicating the order of discovery (a system similar to that

already used forasteroids), so that the fourth comet discovered in the second half of

February 2006, for example, would be designated 2006 D4. Prefixes are also added toindicate the nature of the comet:
http://en.wikipedia.org/wiki/C/1680_V1http://en.wikipedia.org/wiki/C/1882_R1http://en.wikipedia.org/wiki/C/1882_R1http://en.wikipedia.org/wiki/Great_Daylight_Comet_of_1910http://en.wikipedia.org/wiki/Halley's_Comethttp://en.wikipedia.org/wiki/Edmund_Halleyhttp://en.wikipedia.org/wiki/Edmund_Halleyhttp://en.wikipedia.org/wiki/Edmund_Halleyhttp://en.wikipedia.org/wiki/Edmund_Halleyhttp://en.wikipedia.org/wiki/Halley's_Comethttp://en.wikipedia.org/wiki/Comet#cite_note-39%23cite_note-39http://en.wikipedia.org/wiki/Comet#cite_note-KronkEncke-40%23cite_note-KronkEncke-40http://en.wikipedia.org/wiki/Biela's_Comethttp://en.wikipedia.org/wiki/Comet#cite_note-KronkBiela-41%23cite_note-KronkBiela-41http://en.wikipedia.org/wiki/Comet_IRAS-Araki-Alcockhttp://en.wikipedia.org/wiki/IRAShttp://en.wikipedia.org/w/index.php?title=Genichi_Araki&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Genichi_Araki&action=edit&redlink=1http://en.wikipedia.org/wiki/George_Alcockhttp://en.wikipedia.org/wiki/George_Alcockhttp://en.wikipedia.org/w/index.php?title=P/1990_V1&action=edit&redlink=1http://en.wikipedia.org/wiki/D/1993_F2http://en.wikipedia.org/wiki/D/1993_F2http://en.wikipedia.org/wiki/Provisional_designationhttp://en.wikipedia.org/wiki/C/1969_Y1http://en.wikipedia.org/wiki/Perihelionhttp://en.wikipedia.org/wiki/Perihelionhttp://en.wikipedia.org/wiki/Perihelionhttp://en.wikipedia.org/wiki/Roman_numeralhttp://en.wikipedia.org/wiki/C/1969_Y1http://en.wikipedia.org/wiki/Comet#cite_note-arnett-42%23cite_note-arnett-42http://en.wikipedia.org/wiki/International_Astronomical_Unionhttp://en.wikipedia.org/wiki/Asteroidhttp://en.wikipedia.org/wiki/File:Halley%27s_Comet,_1910.JPGhttp://en.wikipedia.org/wiki/C/1680_V1http://en.wikipedia.org/wiki/C/1882_R1http://en.wikipedia.org/wiki/C/1882_R1http://en.wikipedia.org/wiki/Great_Daylight_Comet_of_1910http://en.wikipedia.org/wiki/Halley's_Comethttp://en.wikipedia.org/wiki/Edmund_Halleyhttp://en.wikipedia.org/wiki/Edmund_Halleyhttp://en.wikipedia.org/wiki/Halley's_Comethttp://en.wikipedia.org/wiki/Comet#cite_note-39%23cite_note-39http://en.wikipedia.org/wiki/Comet#cite_note-KronkEncke-40%23cite_note-KronkEncke-40http://en.wikipedia.org/wiki/Biela's_Comethttp://en.wikipedia.org/wiki/Comet#cite_note-KronkBiela-41%23cite_note-KronkBiela-41http://en.wikipedia.org/wiki/Comet_IRAS-Araki-Alcockhttp://en.wikipedia.org/wiki/IRAShttp://en.wikipedia.org/w/index.php?title=Genichi_Araki&action=edit&redlink=1http://en.wikipedia.org/wiki/George_Alcockhttp://en.wikipedia.org/w/index.php?title=P/1990_V1&action=edit&redlink=1http://en.wikipedia.org/wiki/D/1993_F2http://en.wikipedia.org/wiki/Provisional_designationhttp://en.wikipedia.org/wiki/C/1969_Y1http://en.wikipedia.org/wiki/Perihelionhttp://en.wikipedia.org/wiki/Roman_numeralhttp://en.wikipedia.org/wiki/C/1969_Y1http://en.wikipedia.org/wiki/Comet#cite_note-arnett-42%23cite_note-arnett-42http://en.wikipedia.org/wiki/International_Astronomical_Unionhttp://en.wikipedia.org/wiki/Asteroid


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P/ indicates a periodic comet (defined for these purposes as any comet with anorbital period of less than 200 years or confirmed observations at more than one

perihelion passage);

C/ indicates a non-periodic comet (defined as any comet that is notperiodicaccording to the preceding definition);

X/ indicates a comet for which no reliable orbit could be calculated (generally,

historical comets);

D/ indicates a comet which has broken up or been lost, referred to as dark comet;[44]

A/ indicates an object that was mistakenly identified as a comet, but is actually a

minor planet.

For example, Comet Hale-Bopp's designation is C/1995 O1. After their second observed

perihelion passage, periodic comets are also assigned a number indicating the order of

their discovery.[45]So Halley's Comet, the first comet to be identified as periodic, has the

systematic designation 1P/1682 Q1. Comets which first received a minor planetdesignation keep the latter, which leads to some odd names such asP/2004 EW38(Catalina-LINEAR).

There are only five bodies in our Solar System that are cross-listed as both comets and

asteroids: 2060 Chiron (95P/Chiron), 4015 Wilson-Harrington (107P/Wilson-Harrington), 7968 Elst-Pizarro (133P/Elst-Pizarro), 60558 Echeclus (174P/Echeclus), and

118401 LINEAR(176P/LINEAR).

[edit] History of study

[edit] Early observations and thought

Halley's Comet depicted on the Bayeux Tapestry which shows King Harold I being toldof Halley's Comet beforethe Battle of Hastings in 1066.

Before the invention of the telescope, comets seemed to appear out of nowhere in the sky

and gradually vanish out of sight. They were usually considered badomens of deaths of

kings or noble men, or coming catastrophes, or even interpreted as attacks by heavenlybeings against terrestrial inhabitants.[46] From ancient sources, such as Chinese oracle

bones, it is known that their appearances have been noticed by humans for millennia.

Some authorities interpret references to "falling stars" in Gilgamesh, theBook ofRevelation, and the Book of Enoch as references to comets, or possiblybolides. One very
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famous old recording of a comet is the appearance of Halley's Comet on the BayeuxTapestry, which records theNorman conquestofEnglandin AD 1066.[47]

In the first book of his Meteorology,Aristotlepropounded the view of comets that would

hold sway in Western thought for nearly two thousand years. He rejected the ideas of

several earlier philosophers that comets wereplanets, or at least a phenomenon related tothe planets, on the grounds that while the planets confined their motion to the circle of the

Zodiac, comets could appear in any part of the sky.[48]Instead, he described comets as a

phenomenon of the upperatmosphere, where hot, dry exhalations gathered andoccasionally burst into flame. Aristotle held this mechanism responsible for not only

comets, but also meteors, the aurora borealis, and even theMilky Way.[49]

A few later classical philosophers did dispute this view of comets.Seneca the Younger,

in hisNatural Questions, observed that comets moved regularly through the sky and wereundisturbed by the wind, behavior more typical of celestial than atmospheric phenomena.

While he conceded that the other planets do not appear outside the Zodiac, he saw no

reason that a planet-like object could not move through any part of the sky, humanity'sknowledge of celestial things being very limited.[50] However, the Aristotelian viewpoint

proved more influential, and it was not until the 16th century that it was demonstrated

that comets must exist outside the Earth's atmosphere.

In 1577, a bright comet was visible for several months. The Danish astronomerTychoBrahe used measurements of the comet's position taken by himself and other,

geographically separated, observers to determine that the comet had no measurable

parallax. Within the precision of the measurements, this implied the comet must be atleast four times more distant from the earth than the moon. [51]

[edit] Orbital studies

The orbit of the comet of 1680, fit to aparabola, as shown inIsaac Newton'sPrincipia

Although comets had now been demonstrated to be in the heavens, the question of howthey moved through the heavens would be debated for most of the next century. Even

afterJohannes Keplerhad determined in 1609 that the planets moved about the sun in

elliptical orbits, he was reluctant to believe that the laws that governed the motions of the

planets should also influence the motion of other bodieshe believed that comets travelamong the planets along straight lines.Galileo Galilei, although a staunchCopernicanist,

rejected Tycho's parallax measurements and held to the Aristotelian notion of comets

moving on straight lines through the upper atmosphere.[citation needed]

The first suggestion that Kepler's laws of planetary motion should also apply to thecomets was made by William Lowerin 1610.[51]In the following decades other

astronomers, including Pierre Petit, Giovanni Borelli, Adrien Auzout,Robert Hooke,
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Johann Baptist Cysat, and Giovanni Domenico Cassini all argued for comets curvingabout the sun on elliptical or parabolic paths, while others, such as Christian Huygens and

Johannes Hevelius, supported comets' linear motion.[citation needed]

The matter was resolved by thebright cometthat was discovered by Gottfried Kirchon

November 14, 1680. Astronomers throughout Europe tracked its position for severalmonths. In 1681, the Saxon pastorGeorg Samuel Doerfel set forth his proofs that comets

are heavenly bodies moving inparabolasof which the sun is the focus. Then Isaac

Newton, in hisPrincipia Mathematica of 1687, proved that an object moving under theinfluence of his inverse square law ofuniversal gravitation must trace out an orbit shaped

like one of the conic sections, and he demonstrated how to fit a comet's path through the

sky to a parabolic orbit, using the comet of 1680 as an example.[52]

In 1705, Edmond Halley applied Newton's method to twenty-three cometary apparitionsthat had occurred between 1337 and 1698. He noted that three of these, the comets of

1531, 1607, and 1682, had very similarorbital elements, and he was further able to

account for the slight differences in their orbits in terms of gravitational perturbation byJupiterand Saturn. Confident that these three apparitions had been three appearances of

the same comet, he predicted that it would appear again in 17589.[53](Earlier, Robert

Hooke had identified the comet of 1664 with that of 1618,[54]while Giovanni Domenico

Cassini had suspected the identity of the comets of 1577, 1665, and 1680.[55]Both wereincorrect.) Halley's predicted return date was later refined by a team of three French

mathematicians: Alexis Clairaut, Joseph Lalande, andNicole-Reine Lepaute, who

predicted the date of the comet's 1759 perihelion to within one month's accuracy.[56]

When the comet returned as predicted, it became known as Halley's Comet (with the

latter-day designation of 1P/Halley). Its next appearance will be in 2061. See the book2061: Odyssey Three by SirArthur C. Clarke.

Among the comets with short enough periods to have been observed several times in thehistorical record, Halley's Comet is a unique one in that it is consistently bright enough to

be visible to the naked eye while passing through the inner Solar System. Since the

confirmation of the periodicity of Halley's Comet, quite a few other periodic comets havebeen discovered through the use of the telescope. The second comet found to have a

periodic orbit was Encke's Comet (with the official designation of 2P/Encke). During the

period 181921 the German mathematician and physicistJohann Franz Encke computedthe orbits for a series of comets that had been observed in 1786, 1795, 1805, and 1818,

and he concluded that they were same comet, and successfully predicted its return in

1822.[41] By 1900, seventeen comets had been observed through more than one passage

through their perihelions, and then recognized as being periodic comets. As of April2006, 175 comets have achieved this distinction, though several of these seem to have

been destroyed or lost.

[edit] Studies of physical characteristics

Isaac Newton described comets as compact and durable solid bodies moving in oblique

orbits, and their tails as thin streams of vapor emitted by theirnuclei, ignited or heated bythe sun. Newton suspected that comets were the origin of the life-supporting component

of air. Newton also believed that the vapors given off by comets might replenish the

planets' supplies of water (which was gradually being converted into soil by the growthand decay of plants), and the sun's supply of fuel.[citation needed]
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Documents

The Great Comet-Aefie