Editing Comet (section)

=== Modern astronomy ===
Crude attempts at a [[parallax]] measurement of Halley's Comet were made in 1456, but were erroneous.{{Sfn|Sagan|Druyan|1997|p=36}} [[Regiomontanus]] was the first to attempt to calculate [[diurnal parallax]] by observing the [[Great Comet of 1472]]. His predictions were not very accurate, but they were conducted in the hopes of estimating the distance of a comet from Earth.<ref name=":2">{{Cite book |last1=Brandt |first1=John C. |url=https://books.google.com/books?id=CcSUeymd-14C&q=regiomontanus+on+comets&pg=PR7 |title=Introduction to Comets |last2=Chapman |first2=Robert D. |date=2004-03-11 |publisher=Cambridge University Press |isbn=978-0-521-00466-4 |pages=6–11 |language=en}}</ref>

[[File:Brahe notebook.jpg|thumb|Tycho Brahe's sketching of his [[observation]]s of the Great Comet of 1577 in his [[notebook]].]]

In the 16th century, [[Tycho Brahe]] and [[Michael Maestlin]] demonstrated that comets must exist outside of Earth's atmosphere by measuring the parallax of the [[Great Comet of 1577]].<ref>{{Cite journal|last=Barker|first=Peter|date=2002-06-01|title=Constructing Copernicus|journal=Perspectives on Science|volume=10|issue=2|pages=208–227|doi=10.1162/106361402321147531|s2cid=57563317|issn=1063-6145}}</ref> Within the precision of the measurements, this implied the comet must be at least four times more distant than from Earth to the Moon.<ref name="ESO part I">{{cite web |title=A Brief History of Comets I (until 1950) |url=http://www.eso.org/public/events/astro-evt/hale-bopp/comet-history-1.html |publisher=[[European Southern Observatory]] |access-date=14 August 2013}}</ref><ref>{{harvnb|Sagan|Druyan|1997|p=37}}</ref> Based on observations in 1664, [[Giovanni Alfonso Borelli|Giovanni Borelli]] recorded the longitudes and latitudes of comets that he observed, and suggested that cometary orbits may be parabolic.<ref>{{cite journal |title=Giovanni Borelli and the Comets of 1664–65 |journal=Journal for the History of Astronomy |first=Luciano |last=Boschiero |volume=40 |issue=1 |pages=11–30 |date=February 2009 |doi=10.1177/002182860904000103|bibcode=2009JHA....40...11B |s2cid=118350308 }}</ref> Despite being a skilled astronomer, in his 1623 book ''[[The Assayer]]'', [[Galileo Galilei]] rejected Brahe's theories on the parallax of comets and claimed that they may be a mere optical illusion, despite little personal observation.<ref name=":2" /> In 1625, Maestlin's student [[Johannes Kepler]] upheld that Brahe's view of cometary parallax was correct.<ref name=":2" /> Additionally, mathematician [[Jacob Bernoulli]] published a treatise on comets in 1682.

During the [[early modern period]] comets were studied for their astrological significance in medical disciplines. Many healers of this time considered medicine and astronomy to be inter-disciplinary and employed their knowledge of comets and other astrological signs for diagnosing and treating patients.<ref>{{Cite journal|last=Lanuza Navarro|first=Tayra M. C.|date=2006|title=Medical astrology in Spain during the seventeenth century|journal=Cronos (Valencia, Spain)|volume=9|pages=59–84|issn=1139-711X|pmid=18543450}}</ref>

[[Isaac Newton]], in his ''[[Philosophiæ Naturalis Principia Mathematica|Principia Mathematica]]'' of 1687, proved that an object moving under the influence of [[gravity]] by an inverse square law must trace out an orbit shaped like one of the [[conic section]]s, 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.<ref>{{cite book |last=Newton |first=Isaac |author-link=Isaac Newton |chapter=Lib. 3, Prop. 41 |title=Philosophiæ Naturalis Principia Mathematica |publisher=[[Royal Society of London]] |date=1687 |isbn=0-521-07647-1 |title-link=Philosophiæ Naturalis Principia Mathematica}}</ref>
He describes comets as compact and durable solid bodies moving in oblique orbit and their tails as thin streams of vapor emitted by their nuclei, ignited or heated by the Sun. He suspected that comets were the origin of the life-supporting component of air.<ref>{{harvnb|Sagan|Druyan|1997|pp=306–307}}</ref> He pointed out that comets usually appear near the Sun, and therefore most likely orbit it.{{Sfn|Sagan|Druyan|1997|p=26}} On their luminosity, he stated, "The comets shine by the Sun's light, which they reflect," with their tails illuminated by "the Sun's light reflected by a smoke arising from [the coma]".{{Sfn|Sagan|Druyan|1997|p=26}}

[[File:Newton Comet1680.jpg|thumb|290px|The orbit of the comet of 1680, fitted to a [[parabola]], as shown in [[Isaac Newton|Newton]]'s ''[[Philosophiæ Naturalis Principia Mathematica|Principia]]'']]

In 1705, Edmond Halley (1656–1742) applied Newton's method to 23 cometary apparitions that had occurred between 1337 and 1698. He noted that three of these, the comets of 1531, 1607, and 1682, had very similar [[orbital element]]s, and he was further able to account for the slight differences in their orbits in terms of gravitational perturbation caused by Jupiter and [[Saturn]]. Confident that these three apparitions had been three appearances of the same comet, he predicted that it would appear again in 1758–59.<ref name="Halley">{{cite journal |doi=10.1098/rstl.1704.0064 |bibcode=1704RSPT...24.1882H |title=Astronomiae Cometicae Synopsis, Autore Edmundo Halleio apud Oxonienses. Geometriae Professore Saviliano, & Reg. Soc. S |date=1704 |last1=Halleio |first1=E. |journal=Philosophical Transactions of the Royal Society of London |volume=24 |issue=289–304 |pages=1882–1899 |s2cid=186209887 |url=http://rstl.royalsocietypublishing.org/content/24/289-304/1882.full.pdf |archive-url=https://web.archive.org/web/20170430210149/http://rstl.royalsocietypublishing.org/content/24/289-304/1882.full.pdf |archive-date=2017-04-30 |url-status=live|doi-access=free }}</ref> Halley's predicted return date was later refined by a team of three French mathematicians: [[Alexis Clairaut]], [[Joseph Lalande]], and [[Nicole-Reine Lepaute]], who predicted the date of the comet's 1759 perihelion to within one month's accuracy.<ref>On 1758 November 14, Alexis Clairaut announced to the Royal Academy of Sciences in Paris his prediction of the date at which Halley's comet would return:
* Clairaut (January 1759) [https://babel.hathitrust.org/cgi/pt?id=ucm.5324346563;view=1up;seq=44 "Mémoire sur la cométe de 1682,"] ''Le Journal des Sçavans'', pp. 38–45. On p. 44, Clairaut predicts that Halley's comet would return in mid April 1759. From [https://babel.hathitrust.org/cgi/pt?id=ucm.5324346563;view=1up;seq=50 p. 44] (translated from French): " <!-- ... ''il me paroît que la Cométe attendue doit passer à son périhélie vers le milieu du mois d'Avril prochain."'' ( --> ... it seems to me that the expected comet must pass its perihelion towards the middle of next April." On p. 40, Clairaut states that his prediction might be slightly incorrect due to the presence of unknown planets beyond Saturn: "<!-- ''Un corps qui passe dans des régions aussi éloignées, & qui échappe à nos yeux pendant des intervalles aussi longs, pourroit être soumis à des forces totalement inconnues; telles que l'action d'autres Cométes, ou même de quelque planéte toujours trop distante du Soleil pour être jamais apperçue."'' ( -->A body [i.e., Halley's comet] which passes into regions so remote, and which escapes our eyes during such long intervals, might be subjected to totally unknown forces; such as the action of other comets, or even of some planet always too far from the sun to ever be perceived."
On 1759 April 7, the French astronomer [[Joseph-Nicolas Delisle]] announced to the Royal Academy of Sciences in Paris that he and his assistant [[Charles Messier]] had observed the return of Halley's comet, as predicted:
* de l'Isle (June 1759) [https://babel.hathitrust.org/cgi/pt?id=ucm.5324346563;view=1up;seq=360 "Lettre de M. de l'Isle ... contenant la découverte du retour de la Comète de 1682, ... "] (Letter from Mr. de l'Isle ... containing the discovery of the return of the comet of 1682), ''Le Journal des Sçavans'', pp. 356–364.
De l'Isle subsequently admitted that the comet's return had first been seen by a German amateur astronomer and farmer, [[Johann Georg Palitzsch|Georg Palitzsch]]:
* de l'Isle (August 1759) [https://babel.hathitrust.org/cgi/pt?id=ucm.5324346563;view=1up;seq=527 "Seconde lettre de M. de l'Isle,"] ''Le Journal des Sçavans'', pp. 523–529. From p. 526 (translated from French): " <!-- ... ''j'ai reçu une Lettre d'Heidelberg le premier Avril au soir, dans laquelle l'on m'écrit que l'on a publié à Leipsick le 24 Janvier de cette année un Mémoire Allemand dans lequel il est dit que cette Comète a été vue en Saxe par un Paysan, nommé Palisch, le 25 & 26 Décembre de l'année dernière; j'ai bien de la peine à concevoir comment ce Paysan aura pû la découvrir, cette Comète, ... "'' ( --> ... I received a letter from Heidelberg on the first of April in the evening, in which it is written to me that there had been published at Leipzig on the 24th of January of this year a German memoir in which it is said that this comet had been seen in Saxony by a peasant, named Palisch, on the 25th and 26th of December of last year; I can hardly conceive how this peasant could have discovered it, this comet ... "
The story behind the rediscovery of Halley's comet was given by Joseph Lalande in: 
* Delalande, ''Tables astronomiques de M. Halley, ... Et l'Histoire de la Comete de 1759.'' [Astronomical tables of Mr. Halley, ... and the history of the comet of 1759.] (Paris, France: Durand, 1759), [https://babel.hathitrust.org/cgi/pt?id=mdp.39015006990892;view=1up;seq=105 pp. 91 ff.] Lalande acknowledged the contributions of Madame Lepaute to predicting the return of Halley's comet on p. 110. From [https://babel.hathitrust.org/cgi/pt?id=mdp.39015006990892;view=1up;seq=124 p. 110] (translated from French): "<!-- ''... mais il faut convenir que cette suite immense de détails m'eût semblé effrayante, si ''Madame LEPAUTE'', appliquée depuis long-temps & avec succès aux calculs Astronomiques, n'en eût partagé le travail."'' ( --> ... but it must be admitted that this immense series of details would have seemed frightening to me if ''Madame LEPAUTE'', [who has] long applied [herself] successfully to astronomical calculations, had not shared in the work."
See also: 
* Broughton, Peter (1985) "The first predicted return of comet Halley", ''Journal for the History of Astronomy'', '''16''' : 123–132. Available at: [http://adsabs.harvard.edu/full/1985JHA....16..123B Astrophysics Data System]
* Clairaut, [https://books.google.com/books?id=WQRbq4SA_zkC&pg=PP7''Théorie du mouvement des comètes,'' ...] [Theory of the movement of comets, ...] (Paris, France: Michel Lambert, 1760); see especially the preface.</ref>{{sfn|Sagan|Druyan|1997|p=93}} When the comet returned as predicted, it became known as Halley's Comet.<ref>{{cite book |url=https://books.google.com/books?id=DFgMAaU3vA8C&pg=PA35 |page=35 |title=The Greatest Comets in History: Broom Stars and Celestial Scimitars |isbn=978-0-387-09513-4 |last=Wong |first=Yau-Chuen |date=2008|publisher=Springer }}</ref>
{{Quote box |quote=From his huge vapouring train perhaps to shake<br />Reviving moisture on the numerous orbs,<br />Thro' which his long ellipsis winds; perhaps<br />To lend new fuel to declining suns,<br />To light up worlds, and feed th' ethereal fire. |source=[[James Thomson (poet, born 1700)|James Thomson]] ''[[The Seasons (Thomson poem)|The Seasons]]'' (1730; 1748)<ref>{{cite book |url=https://books.google.com/books?id=F--di9y22yUC&pg=PA67 |title=The Background of Thomson's Seasons |isbn=978-0-8166-5950-0 |page=67 |last=McKillop |first=Alan Dugald |date=1942|publisher=U of Minnesota Press }}</ref> |style=padding: 8px 12px;}}

As early as the 18th century, some scientists had made correct hypotheses as to comets' physical composition. In 1755, [[Immanuel Kant]] hypothesized in his ''[[Universal Natural History and Theory of the Heavens|Universal Natural History]]'' that comets were condensed from "primitive matter" beyond the known planets, which is "feebly moved" by gravity, then orbit at arbitrary inclinations, and are partially vaporized by the Sun's heat as they near perihelion.{{Sfn|Sagan|Druyan|1997|pp=84–87}} In 1836, the German mathematician [[Friedrich Wilhelm Bessel]], after observing streams of vapor during the appearance of Halley's Comet in 1835, proposed that the [[jet force]]s of evaporating material could be great enough to significantly alter a comet's orbit, and he argued that the non-gravitational movements of Encke's Comet resulted from this phenomenon.<ref>{{harvnb|Sagan|Druyan|1997|p=126}}</ref>

In the 19th century, the Astronomical Observatory of Padova was an epicenter in the observational study of comets. Led by [[Giovanni Santini]] (1787–1877) and followed by Giuseppe Lorenzoni (1843–1914), this observatory was devoted to classical astronomy, mainly to the new comets and planets orbit calculation, with the goal of compiling a catalog of almost ten thousand stars. Situated in the Northern portion of Italy, observations from this observatory were key in establishing important geodetic, geographic, and astronomical calculations, such as the difference of longitude between Milan and Padua as well as Padua to Fiume.<ref>{{Cite journal|last=Pigatto|first=Luisa|date=December 2009|title=The correspondence of Giovanni Santini and Giuseppe Lorenzoni, directors of the Astronomical Observatory of Padua in the 19th Century|journal=Annals of Geophysics|volume=52|pages=595–604}}</ref> Correspondence within the observatory, particularly between Santini and another astronomer Giuseppe Toaldo, mentioned the importance of comet and planetary orbital observations.<ref>Pigatto, L. (1988): Santini e gli strumenti della Specola, in Giovanni Santini astronomo, "Atti e Memorie dell'Accademia Patavina di Scienze, Lettere ed Arti", (Padova), XCIX (1986–1987), 187–198.</ref>

In 1950, [[Fred Lawrence Whipple]] proposed that rather than being rocky objects containing some ice, comets were icy objects containing some dust and rock.<ref name="Whipple">{{cite journal |doi=10.1086/145272 |title=A comet model. I. The acceleration of Comet Encke |date=1950 |last1=Whipple |first1=F. L. |journal=The Astrophysical Journal |volume=111 |pages=375 |bibcode=1950ApJ...111..375W}}</ref> This "dirty snowball" model soon became accepted and appeared to be supported by the observations of an armada of [[spacecraft]] (including the [[European Space Agency]]'s ''[[Giotto mission|Giotto]]'' probe and the Soviet Union's ''[[Vega 1]]'' and ''[[Vega 2]]'') that flew through the coma of Halley's Comet in 1986, photographed the nucleus, and observed jets of evaporating material.<ref>{{cite book |url=https://books.google.com/books?id=E4NfZ9FDcc8C&pg=PA156 |page=156 |title=Magic Universe:A Grand Tour of Modern Science |isbn=978-0-19-162235-9 |last1=Calder |first1=Nigel |date=13 October 2005|publisher=OUP Oxford }}</ref>

On 22 January 2014, [[European Space Agency|ESA scientists]] reported the detection, for the first definitive time, of [[water vapor]] on the [[dwarf planet]] [[Ceres (dwarf planet)|Ceres]], the largest object in the asteroid belt.<ref name="KüppersO'Rourke2014">{{cite journal |last1=Küppers |first1=Michael |last2=O'Rourke |first2=Laurence |last3=Bockelée-Morvan |first3=Dominique|author3-link=Dominique Bockelée-Morvan |last4=Zakharov |first4=Vladimir |last5=Lee |first5=Seungwon |last6=von Allmen |first6=Paul |last7=Carry |first7=Benoît |last8=Teyssier |first8=David |last9=Marston |first9=Anthony |last10=Müller |first10=Thomas |last11=Crovisier |first11=Jacques |last12=Barucci |first12=M. Antonietta |last13=Moreno |first13=Raphael |title=Localized sources of water vapour on the dwarf planet (1) Ceres |journal=Nature |volume=505 |issue=7484 |date=2014 |pages=525–527 |issn=0028-0836 |doi=10.1038/nature12918 |bibcode=2014Natur.505..525K |pmid=24451541|s2cid=4448395 }}</ref> The detection was made by using the [[Far-infrared astronomy|far-infrared abilities]] of the [[Herschel Space Observatory]].<ref name="NASA-20140122">{{cite web |last1=Harrington |first1=J.D. |title=Herschel Telescope Detects Water on Dwarf Planet – Release 14-021 |url=http://www.nasa.gov/press/2014/january/herschel-telescope-detects-water-on-dwarf-planet |date=22 January 2014 |publisher=[[NASA]] |access-date=22 January 2014}}</ref> The finding is unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids."<ref name="NASA-20140122" /> On 11 August 2014, astronomers released studies, using the [[Atacama Large Millimeter Array|Atacama Large Millimeter/Submillimeter Array (ALMA)]] for the first time, that detailed the distribution of [[Hydrogen cyanide|HCN]], [[Hydrogen isocyanide|HNC]], [[Formaldehyde|{{chem2|H2CO}}]], and dust inside the [[Coma (cometary)|comae]] of comets [[C/2012 F6 (Lemmon)]] and [[Comet ISON|C/2012 S1 (ISON)]].<ref name="NASA-20140811">{{cite web |url=http://www.nasa.gov/press/2014/august/goddard/nasa-s-3-d-study-of-comets-reveals-chemical-factory-at-work |title=Release 14-038: NASA's 3-D Study of Comets Reveals Chemical Factory at Work |publisher=[[NASA]] |last1=Zubritsky |first1=Elizabeth |last2=Neal-Jones |first2=Nancy |name-list-style=amp |date=11 August 2014 |access-date=12 August 2014}}</ref><ref name="AJL-20140811">{{cite journal |last=Cordiner |first=M. A. |title=Mapping the Release of Volatiles in the Inner Comae of Comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) Using the Atacama Large Millimeter/Submillimeter Array |date=11 August 2014 |journal=[[The Astrophysical Journal]] |volume=792 |number=1 |doi=10.1088/2041-8205/792/1/L2 |display-authors=etal |arxiv=1408.2458 |bibcode=2014ApJ...792L...2C |pages=L2|s2cid=26277035 }}</ref>