Editing Solar wind (section)

===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>