Comet

{{Astronomy}}
'''Comets''' are a specific kind of minor [[Solar System]] body that shed gas and particles when they get close to the [[Sun]]. As a result, a comet gets enveloped with an expanding hazy cloud (called a coma) and grows a tail pointing away from the Sun, driven by the solar wind. This increases its brightness several times, as the coma and the tail are much larger and reflect sunlight better than the comet nucleus (core) &mdash; the actual solid body of the comet.

As comets are thought to be composed of rock, dust, and ice (not only water, but also methane, ammonia, and other compounds), they are sometimes called "dirty snowballs" in popular-science media, though this may be misleading. The exact composition probably varies from comet to comet and "snowy dirtballs" may be a better description.

==Properties==
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Most comets never become bright enough to be visible to the naked eye.

Most comets move on orbits with a very high eccentricity &mdash; either a very elongated ellipse, or a parabola or hyperbola.
[[File:Halley's Comet, 1910.JPG|thumb|Halley's Comet in 1910.]]
[[File:Shoemaker-Levy 9 on 1994-05-17.png|thumb|The string of Shoemaker-Levy fragments in May 1994.]]
[[File:Jupiter showing SL9 impact sites.jpg|thumb|Shoemaker-Levy impact sites on Jupiter.]]
[[File:Comet Hale-Bopp 1995O1.jpg|thumb|Comet Hale-Bopp in 1997]]
[[File:17P_Holmes_Composite19_Nup.jpg|thumb|Composite photo showing the path and expansion of Comet Holmes between October 2007 and March 2008]]

==Comet woo==
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===Creationism===
[[Young Earth creationist]]s challenge Old Earth estimates of the age of the Solar System by arguing that as comets lose material when they approach the Sun, all comets must have disappeared by now if the Solar System was old.<ref>[http://www.talkorigins.org/indexcc/CE/CE261.html Old Comets] - [[Talk.origins]]</ref><ref>[http://www.talkorigins.org/faqs/hovind/howgood-yea.html#proof3 How good are those young earth arguments: Hovind's 'proofs'] - Talk.origins</ref> This is partially true; comets do lose material and old comets have lost their volatile material and no longer produce a tail, but the number of comets that cross into the inner Solar System is constantly replenished from "stores" in the Kuiper Belt and the Oort Cloud at its edge. (This, of course, has prompted creationists to challenge the existence of these swarms.<ref>[http://www.talkorigins.org/indexcc/CE/CE261_1.html Reality of Kuiper Belt and Oort Cloud] - Talk.origins</ref>)

===Harbingers of doom===
Comets have a long history of being [[superstition|misinterpreted]] as portents of doom sent from the [[gods]]. In the [[Middle Ages]] scholars viewed comets as warnings from the Heavens that an "[[Act of God]]" (also known to the [[reality-based community]] as a "natural disaster") was about to take place, up to and including a [[plague]] [[epidemic]].<ref name="convo">"[https://theconversation.com/comets-omens-and-fear-understanding-plague-in-the-middle-ages-141327 Comets, omens and fear: understanding plague in the Middle Ages]" - ''The Conversation''. Published June 24, 2020 at 4:59 PM (BST).</ref> The Medieval [[English]] scholar {{wpl|Bede}} wrote in his treatise on [[natural philosophy]] ''De Rerum Natura'' that comets were like "stars with flames like hair. They are born suddenly, portending a change of royal power or plague or wars or winds or heat."<ref name="convo" />
 	
According to legend, the {{wpl|Aztec}} emperor {{wpl|Montezuma}} observed eight omens that supposedly heralded the coming of the [[Spaniard]]s and the fall of the {{wpl|Aztec Empire||.}} One of these portents of doom{{efn|The earliest one in fact, occurring a full ten years before the Spaniards made landfall in 1519.}} was a "fire plume" that appeared suddenly in the night sky. The appearance of the fire plume was apparently a cause of great distress among the people of {{wpl|Mesoamerica||.}}{{efn|If only they knew how [[Native American genocide|right]] they were...}}<ref>"[https://mexicounexplained.com/8-omens-montezuma-end-aztec-empire/ The Eight Omens of Montezuma and the End of the Aztec Empire]" - Mexico Unexplained</ref>

As there is no [[absence of evidence|known]] [[physical]] process that can lead to comets millions of miles out in [[space]] [[magic|affecting]] things here on [[Earth]],{{efn|At least without an asteroid impact.}} any claim that [[astrology|random chunks of space debris]] popping up in the night sky will lead to you getting sick can be safely [[Hitchens' razor|dismissed]].

===Nostradamus===
[[Nostradamus]] directly mentions a comet once in his ''Prophecies'', in quatrain 2:62:
{{quotebox|Mabus puis tost alors mourra viendra,<br/>
De gens & bestes vne horrible deffaite,<br/>
Puis tout à coup la vengeance on verra,<br/>
Cent, main, soif, faim, quand courra la comette.<br/>

Mabus then will soon die, there will come<br/>
Of people and beasts a horrible rout:<br/>
Then suddenly one will see vengeance,<br/>
Hundred, hand, thirst, hunger when the comet will run.<ref>Text from [http://www.sacred-texts.com/nos/mrg/nosmrg02.htm here], no name of the English translator</ref>}}

Expect this quote to be dug out every time a comet catches the attention of the [[conspiracy]] crowd. Nobody knows who "Mabus" is, though we're pretty sure it's not [[Dennis Markuze]].

==Notable comets==
===Halley===
Halley's Comet (formally 1P/Halley) is probably the most well-known comet, as it is the only one visible with the naked eye that appears with some regularity. Its orbital period &mdash; about 76 years &mdash; is short enough to allow people to see it twice in their lifetime. There are records of its appearances since the third century [[BCE]]. During the spectacularly close approach in 1910, the Earth passed through its tail, sparking an [[List of predictions of the end of the world|end-of-the-world scare]], as spectroscopy was applied for the first time to a comet and found cyanogen, a poisonous gas, in the tail. Some entrepreneurs took advantage of the situation and started selling "comet pills" and other comet counter-measures.<ref>[http://www.wired.com/2015/01/fantastically-wrong-halleys-comet/ Fantastically Wrong: That Time People Thought a Comet Would Gas Us All to Death] by Matt Simon (01.07.15 6:30 am) ''Wired''.</ref>

===Shoemaker-Levy 9===
Comet D/1993 F2 (Shoemaker-Levy) broke up and collided with [[Jupiter]] in July 1994, leaving several spectacular "bruises" on its cloud layers. This was widely reported and raised some awareness about the possibility of a comet impacting Earth and may have been the inspiration for the ''Deep Impact''/''Armageddon'' movie pair a few years later.

===Hale-Bopp===
Comet C/1995 O1 (Hale–Bopp) was a bright, spectacular comet that reached perihelion in 1997 and was widely observed around the world. It is notoriously connected to the [[Heaven's Gate]] [[UFO]] [[cult]] [[suicide]]s. Two years earlier, [[Nancy Lieder]] claimed that the comet was a hoax to distract the attention from the incoming [[Planet X]].<ref>The relevant pages in the Zeta Talk website has been edited, but Google Groups has archived e-mails citing it.[http://groups.google.com/group/sci.astro.amateur/browse_frm/thread/6ffea21e1fafcea9]</ref>

===C/2010 X1 (Elenin)===
{{main|Comet Elenin}}
An otherwise unremarkable comet that for some reason attracted the attention of the [[Planet X]]/[[Nibiru]]/[[2012 apocalypse]] crowd. After generating several terabytes of [[bullshit]] on conspiracy websites and YouTube videos, it made a lot of people look 
dumb
 even dumber when it didn't survive its close approach to the Sun. Rest in Pieces, you little comet!

===C/2012 S1 (ISON)===
Discovered in 2012, this comet attracted the attention of doom-mongers with the ''possibility'' that it might become extremely bright. (According to some scientific predictions, at one point as bright as the full [[Moon]], if it survived perihelion.<ref>[http://www.newscientist.com/blogs/shortsharpscience/2012/09/newly-spotted-comet-may-outshi.html Newly spotted comet may outshine the full moon], ''Short Sharp Science'', ''New Scientist Blogs'', 25 September 2012</ref> This ultimately didn't happen, but as we know, comets are notoriously fickle.) Its perihelion was in November 2013, and people like [[James McCanney]] began piling on nice and early<ref>[http://www.jmccsci.com/Comet%20C2012%20S1%20%28ISON%29%20Sub-page.HTM Comet C/2012 S1 (ISON) Sub- page], jamesmccanneyscience.com</ref> and it looked like there would be a repeat of the Elenin hysteria. ISON mostly broke up at perihelion, and though a tiny remnant dragged on a bit longer, it eventually faded out.<ref>[http://www.slate.com/blogs/bad_astronomy/2013/12/01/comet_ison_post_mortem.html Comet ISON post-mortem] - ''[[Bad Astronomy]]''</ref>

===67P/Churyumov–Gerasimenko===
A run-of-the-mill comet of special interest just because it has been the destination of the European {{wpl|Rosetta mission|''Rosetta mission||,}} composed of an orbiter (''Rosetta'') and a lander ''(Philae)'' that landed on it in November 2014 (the first man made object that has landed on a comet). The mission was ended in September 2016, crashing ''Rosetta'' into the bone-shaped comet (no woo ''so far'' on this one).<ref>[https://solarsystem.nasa.gov/missions/rosetta-philae/in-depth/ In Depth: ''Rosetta'' and ''Philae''] - NASA</ref>

==See also==
*[[Tunguska event]]

==Notes==
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==References==
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[[Category:Astronomy]]

Categories: Astronomy