Editing Solar wind (section)

==History==
===Observations from Earth===
The existence of particles flowing outward from the [[Sun]] to the [[Earth]] was first suggested by British astronomer [[Richard Christopher Carrington|Richard C. Carrington]]. In 1859, Carrington and [[Richard Hodgson (publisher)|Richard Hodgson]] independently made the first observations of what would later be called a [[solar flare]]. This is a sudden, localised increase in brightness on the solar disc, which is now known<ref>{{Cite journal|last1=Cliver|first1=Edward W.|last2=Dietrich|first2=William F.|date=2013-01-01|title=The 1859 space weather event revisited: limits of extreme activity|journal=Journal of Space Weather and Space Climate|language=en|volume=3|pages=A31|doi=10.1051/swsc/2013053|issn=2115-7251|bibcode = 2013JSWSC...3A..31C |doi-access=free}}</ref> to often occur in conjunction with an episodic ejection of material and magnetic flux from the Sun's atmosphere, known as a [[coronal mass ejection]]. The following day, a [[September 1859 geomagnetic storm|powerful geomagnetic storm]] was observed, and Carrington suspected that there might be a connection; the [[geomagnetic storm]] is now attributed to the arrival of the coronal mass ejection in near-Earth space and its subsequent interaction with the Earth's [[magnetosphere]]. Irish academic [[George Francis FitzGerald|George FitzGerald]] later suggested that matter was being regularly accelerated away from the Sun, reaching the Earth after several days.<ref name=meyer-vernet>{{cite book
 | first=Nicole | last=Meyer-Vernet | date=2007
 | title=Basics of the Solar Wind
 | publisher=Cambridge University Press
 | isbn=978-0-521-81420-1 }}</ref>

[[Image:Birkeland-anode-globe-fig259.jpg|thumb|upright=1.15|Laboratory simulation of the magnetosphere's influence on the solar wind; these aurora-like [[Birkeland current]]s were created in a [[terrella]], a magnetised anode globe in an evacuated chamber.]]

In 1910, British astrophysicist [[Arthur Eddington]] essentially suggested the existence of the solar wind, without naming it, in a footnote to an article on [[Comet Morehouse]].<ref name=durham>{{cite news
| first=Ian T. | last=Durham | date=2006
| title=Rethinking the History of Solar Wind Studies: Eddington's Analysis of Comet Morehouse
| url=http://rsnr.royalsocietypublishing.org/content/60/3/261.abstract
| journal=Notes and Records of the Royal Society | volume=60 | pages=261–270}}</ref> Eddington's proposition was never fully embraced, even though he had also made a similar suggestion at a [[Royal Institution]] address the previous year, in which he had postulated that the ejected material consisted of electrons, whereas in his study of Comet Morehouse he had supposed them to be [[ion]]s.<ref name=durham/>

The idea that the ejected material consisted of both ions and electrons was first suggested by Norwegian scientist [[Kristian Birkeland]].<ref>{{cite book |title=Kristian Birkeland: The First Space Scientist |first1=Alv |last1=Egeland |first2=William J. |last2=Burke |publisher=Springer, Dordrecht, The Netherlands |page=[https://archive.org/details/kristianbirkelan0000egel/page/80 80] |year=2005 |url=https://archive.org/details/kristianbirkelan0000egel|url-access=registration |isbn=978-1-4020-3294-3}}</ref> His geomagnetic surveys showed that auroral activity was almost uninterrupted. As these displays and other geomagnetic activity were being produced by particles from the Sun, he concluded that the Earth was being continually bombarded by "rays of electric corpuscles emitted by the Sun".<ref name="meyer-vernet" /> He proposed in 1916 that, "From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, but of both kinds"; in other words, the solar wind consists of both negative electrons and positive ions.<ref>Kristian Birkeland, "Are the Solar Corpuscular Rays that penetrate the Earth's Atmosphere Negative or Positive Rays?" in ''Videnskapsselskapets Skrifter'', I Mat – Naturv. Klasse No.1, Christiania, 1916.</ref> Three years later, in 1919, British physicist [[Frederick Lindemann, 1st Viscount Cherwell|Frederick Lindemann]] also suggested that the Sun ejects particles of both polarities: protons as well as electrons.<ref>''Philosophical Magazine'', Series 6, Vol. 38, No. 228, December 1919, 674 (on the Solar Wind)</ref>

Around the 1930s, scientists had concluded that the temperature of the [[solar corona]] must be a million degrees [[Anders Celsius|Celsius]] because of the way it extended into space (as seen during a total [[solar eclipse]]). Later [[Spectroscopy|spectroscopic]] work confirmed this extraordinary temperature to be the case. In the mid-1950s, British mathematician [[Sydney Chapman (mathematician)|Sydney Chapman]] calculated the properties of a gas at such a temperature and determined that the corona being such a superb conductor of heat, it must extend way out into space, beyond the orbit of Earth. Also in the 1950s, German astronomer [[Ludwig Biermann]] became interested in the fact that the tail of a [[comet]] always points away from the Sun, regardless of the direction in which the comet is travelling. Biermann postulated that this happens because the Sun emits a steady stream of particles that pushes the comet's tail away.<ref>{{cite journal |author=Ludwig Biermann |title=Kometenschweife und solare Korpuskularstrahlung |journal=Zeitschrift für Astrophysik |volume=29 |pages=274 |date=1951|bibcode = 1951ZA.....29..274B }}</ref> German astronomer [[Paul Oswald Ahnert|Paul Ahnert]] is credited (by Wilfried Schröder) as being the first to relate solar wind to the direction of a comet's tail based on observations of the comet Whipple–Fedke (1942g).<ref>{{cite journal|last=Schröder |first=Wilfried |title=Who first discovered the solar wind? |date=1 December 2008 |journal=Acta Geodaetica et Geophysica Hungarica |volume=43 |issue=4 |pages=471–472 |doi=10.1556/AGeod.43.2008.4.8|bibcode=2008AGGH...43..471S |s2cid=130425794 }}</ref>

American astrophysicist [[Eugene Parker]] realised that heat flowing from the Sun in Chapman's model, and the comet tail blowing away from the Sun in Biermann's hypothesis, had to be the result of the same phenomenon which he termed the "solar wind".<ref>{{cite web|title=THE SOLAR WIND AND MAGNETOSPHERIC DYNAMICS|author=Christopher T. Russell|work=Institute of Geophysics and Planetary Physics University of California, Los Angeles|url=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/solwind_magsphere/|access-date=2007-02-07|archive-date=August 13, 2018|archive-url=https://web.archive.org/web/20180813043542/http://www-ssc.igpp.ucla.edu/personnel/russell/papers/solwind_magsphere/|url-status=dead}}</ref><ref>{{cite news | last=Roach | first=John | title=Astrophysicist Recognized for Discovery of Solar Wind | work=National Geographic Society | date=August 27, 2003 | url=http://news.nationalgeographic.com/news/2003/08/0827_030827_kyotoprizeparker.html | access-date=2006-06-13 |archive-url=https://web.archive.org/web/20030830010454/http://news.nationalgeographic.com/news/2003/08/0827_030827_kyotoprizeparker.html |archive-date=August 30, 2003 |url-status=dead}}</ref> In 1957, Parker showed that although the Sun's corona is strongly attracted by solar gravity, it is such a good conductor of heat that it is still very hot at large distances from the Sun. As solar gravity weakens with increasing distance from the Sun, the outer coronal atmosphere is able to escape [[Supersonic speed|supersonically]] into interstellar space. Parker was also the first person to notice that the weakening influence of the Sun's gravity has the same effect on [[hydrodynamic]] flow as a [[de Laval nozzle]], inciting a transition from [[Speed of sound|subsonic]] to supersonic flow.<ref name="Parker 1958">{{cite journal |last=Parker |first=Eugene N. |bibcode=1958ApJ...128..664P |title=Dynamics of the Interplanetary Gas and Magnetic Fields |journal=The Astrophysical Journal |volume=128 |pages=664–676 |date=November 1958 |doi=10.1086/146579}}</ref> There was strong opposition to Parker's hypothesis on the solar wind; the paper he submitted to ''[[The Astrophysical Journal]]'' in 1958<ref name="Parker 1958" /> was rejected by two reviewers, before being accepted by the editor [[Subrahmanyan Chandrasekhar]].<ref>{{Citation | title = The martial art of scientific publication | year = 1997 | last1 = Parker | first1 = E. N. | journal = [[Eos (magazine)|EOS Transactions]] | volume = 78 | issue = 37 | pages = 391–395 | doi = 10.1029/97EO00251 | bibcode = 1997EOSTr..78..391P}}</ref><ref>{{Cite web |date=2018-07-31 |title=NASA mission honors pioneering UChicago physicist {{!}} University of Chicago News |url=https://news.uchicago.edu/story/nasa-mission-honors-pioneering-uchicago-physicist |access-date=2024-04-30 |website=news.uchicago.edu |language=en}}</ref>

===Observations from space===
In January 1959, the [[Soviet Union|Soviet]] spacecraft ''[[Luna 1]]'' first directly observed the solar wind and measured its strength,<ref>{{cite book|title=Russian Planetary Exploration: History, Development, Legacy and Prospects |last=Harvey |first=Brian |author-link=Brian Harvey (author) |year=2007 |publisher=Springer |page=26 |isbn=978-0-387-46343-8}}</ref><ref>{{cite web|url=https://www.daviddarling.info/encyclopedia/L/Luna.html |title=Luna |last=Darling |first=David J. |author-link=David J. Darling |website=Internet Encyclopedia of Science |access-date=2020-10-02}}</ref><ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1959-012A |title=Luna 1 |publisher=[[NASA]] NASA Space Science Data Coordinated Archive |access-date=2007-08-04}}</ref> using hemispherical ion traps. The discovery, made by {{ILL|Konstantin Gringauz|ru|Грингауз, Константин Иосифович}}, was verified by ''[[Luna 2|Luna&nbsp;2]]'', ''[[Luna 3|Luna&nbsp;3]]'', and the more distant measurements of ''[[Venera 1|Venera&nbsp;1]]''. Three years later, a similar measurement was performed by American geophysicist [[Marcia Neugebauer]] and collaborators using the ''[[Mariner 2|Mariner&nbsp;2]]'' spacecraft.<ref>{{cite journal |last1=Neugebauer|first1=M.|author1-link=Marcia Neugebauer|last2=Snyder|first2=C. W.|name-list-style=amp |title=Solar Plasma Experiment |journal=Science |volume=138 |pages=1095–1097 |date=1962 | doi = 10.1126/science.138.3545.1095-a |pmid=17772963 |issue=3545|bibcode = 1962Sci...138.1095N |s2cid=24287222}}</ref>

The first numerical simulation of the solar wind in the solar corona, including [[Magnetic field|closed and open field lines]], was performed by Pneuman and Kopp in 1971. The [[magnetohydrodynamics]] equations in [[steady state]] were solved iteratively starting with an initial [[dipole|dipolar]] configuration.<ref>{{cite journal |author=G. W. Pneuman|author2=R. A. Kopp|name-list-style=amp |title=Gas-magnetic field interactions in the solar corona |journal=Solar Physics |volume=18 |issue=2 |pages=258 |date=1971 | doi = 10.1007/BF00145940 |bibcode=1971SoPh...18..258P|s2cid=120816610}}</ref>

In 1990, the [[Ulysses (spacecraft)|''Ulysses'']] probe was launched to study the solar wind from high solar latitudes. All prior observations had been made at or near the Solar System's [[ecliptic]] plane.<ref>{{cite web|url=http://ulysses.jpl.nasa.gov/science/index.html|title=Solar System Exploration: Missions: By Target: Mars: Present|work=Solar System Exploration|url-status=dead|archive-url=https://web.archive.org/web/20080920221334/http://ulysses.jpl.nasa.gov/science/index.html|archive-date=2008-09-20}}</ref>

In the late 1990s, the Ultraviolet Coronal Spectrometer (UVCS) instrument on board the [[Solar and Heliospheric Observatory|SOHO]] spacecraft observed the acceleration region of the fast solar wind emanating from the poles of the Sun and found that the wind accelerates much faster than can be accounted for by thermodynamic expansion alone. Parker's model predicted that the wind should make the transition to supersonic flow at an altitude of about four [[solar radius|solar radii]] (approx. 3,000,000&nbsp;km) from the [[photosphere]] (surface); but the transition (or "sonic point") now appears to be much lower, perhaps only one solar radius (approx. 700,000&nbsp;km) above the photosphere, suggesting that some additional mechanism accelerates the solar wind away from the Sun. The acceleration of the fast wind is still not understood and cannot be fully explained by Parker's theory. However, the gravitational and electromagnetic explanation for this acceleration is detailed in an earlier paper by 1970 [[List of Nobel laureates in Physics|Nobel laureate in Physics]], [[Hannes Alfvén]].<ref>{{cite web | url=https://archive.org/download/RotationOfMagnetizedSphereWithApplicationToSolarRadiation/AlfvenH.RemarksOnTheRotationOfAMagnetizedSphereWithApplicationToSolarRadiationarkivForMatematikAstronomiOchFysik28a61942.pdf |archive-url=https://web.archive.org/web/20191004234804/http://ia802901.us.archive.org/14/items/RotationOfMagnetizedSphereWithApplicationToSolarRadiation/AlfvenH.RemarksOnTheRotationOfAMagnetizedSphereWithApplicationToSolarRadiationarkivForMatematikAstronomiOchFysik28a61942.pdf |url-status=live |title=Remarks on the Rotation of a Magnetized Sphere with Application to Solar Radiation |archive-date=2019-10-04}}</ref><ref>{{cite journal |author=Hannes Alfvén |title=Remarks on the Rotation of a Magnetized Sphere with Application to Solar Radiation |journal=Arkiv för Matematik, Astronomi och Fysik |volume=28A |issue=6 |pages=1–9 |date=1942}}</ref>

From May 10 to May 12, 1999, NASA's [[Advanced Composition Explorer]] (ACE) and [[WIND (spacecraft)|WIND]] spacecraft observed a 98% decrease of solar wind density. This allowed energetic electrons from the Sun to flow to Earth in narrow beams known as "[[strahl (astronomy)|strahl]]", which caused a highly unusual "polar rain" event, in which a visible [[Aurora (astronomy)|aurora]] appeared over the North Pole. In addition, Earth's magnetosphere increased to between 5 and 6 times its normal size.<ref>{{Cite web |title=The Day the Solar Wind Disappeared |publisher=NASA Science |url=https://science.nasa.gov/science-news/science-at-nasa/1999/ast13dec99_1/ |date=December 13, 1999 |access-date=October 5, 2010 |archive-date=November 22, 2021 |archive-url=https://web.archive.org/web/20211122004707/https://science.nasa.gov/science-news/science-at-nasa/1999/ast13dec99_1 |url-status=dead }}</ref>

The [[STEREO]] mission was launched in 2006 to study coronal mass ejections and the solar corona, using [[stereoscopy]] from two widely separated imaging systems. Each STEREO spacecraft carried two heliospheric imagers:  highly sensitive wide-field cameras capable of imaging the solar wind itself, via [[Thomson scattering]] of sunlight off of free electrons. Movies from STEREO revealed the solar wind near the ecliptic, as a large-scale turbulent flow.
[[file:Solar wind at Voyager 1.png|thumb|upright=1.3|Plot showing a dramatic decrease in the rate of solar wind particle detection by ''Voyager 1'']]

On December 13, 2010, ''[[Voyager 1]]'' determined that the velocity of the solar wind, at its location {{convert|10.8|e9mi|e9km|abbr=off}} from Earth had slowed to zero. "We have gotten to the point where the wind from the Sun, which until now has always had an outward motion, is no longer moving outward; it is only moving sideways so that it can end up going down the tail of the heliosphere, which is a comet-shaped-like object", said Voyager project scientist Edward Stone.<ref>{{Cite news |title=Voyager Near Solar System Edge|publisher=BBC|url=https://www.bbc.co.uk/news/science-environment-11988466|date=December 13, 2010 |access-date=December 14, 2010|work=BBC News|last1=Amos|first1=Jonathan}}</ref><ref>{{Cite web |title=NASA Probe Sees Solar Wind Decline En Route To Interstellar Space|publisher=NASA |url=http://www.nasa.gov/home/hqnews/2010/dec/HQ_10-334_Voyager_Voyages.html |date=December 13, 2010 |access-date=December 14, 2010}}</ref>

In 2018, NASA launched the ''[[Parker Solar Probe]]'', named in honor of American astrophysicist Eugene Parker, on a mission to study the structure and dynamics of the solar corona, in an attempt to understand the mechanisms that cause particles to be heated and accelerated as solar wind. During its seven-year mission, the probe will make twenty-four orbits of the Sun, passing further into the corona with each orbit's [[perihelion]], ultimately passing within 0.04 [[astronomical units]] of the Sun's surface. It is the first NASA spacecraft named for a living person, and Parker, at age 91, was on hand to observe the launch.<ref name="NYT-20180812-kc">{{cite news|last=Chang|first=Kenneth|title=Parker Solar Probe Launches on NASA Voyage to 'Touch the Sun'|url=https://www.nytimes.com/2018/08/11/science/parker-solar-probe-launch.html|date=August 12, 2018|work=[[The New York Times]]|access-date=August 14, 2018}}</ref>