Editing Astronomy (section)

=== Solar astronomy ===
[[File:Uvsun trace big.jpg|thumb|An [[ultraviolet]] image of the Sun's active [[photosphere]] as viewed by the NASA's [[TRACE]] space telescope.]]
[[File:Observatórium Lomnický štít 1.jpg|thumb|Solar observatory [[Lomnický štít]] ([[Slovakia]]) built in 1962]]
{{See also|Solar telescope}}
At a distance of about eight light-minutes, the most frequently studied star is the [[Sun]], a typical main-sequence [[dwarf star]] of [[stellar class]] G2 V, and about 4.6 billion years (Gyr) old. The Sun is not considered a [[variable star]], but it does undergo periodic changes in activity known as the [[sunspot cycle]]. This is an 11-year oscillation in [[Wolf number|sunspot number]]. Sunspots are regions of lower-than-average temperatures that are associated with intense magnetic activity.<ref name="solar FAQ">{{cite web|url=http://www.talkorigins.org/faqs/faq-solar.html|title=The Solar FAQ|last=Johansson|first=Sverker|author-link=Sverker Johansson|date=27 July 2003|publisher=Talk.Origins Archive|access-date=11 August 2006|archive-url=https://web.archive.org/web/20060907235636/http://www.talkorigins.org/faqs/faq-solar.html|archive-date=7 September 2006 |url-status=live}}</ref>

The Sun has steadily increased in luminosity by 40% since it first became a main-sequence star. The Sun has also undergone periodic changes in luminosity that can have a significant impact on the Earth.<ref name="Environmental issues : essential primary sources.">{{cite web|url=http://catalog.loc.gov/cgi-bin/Pwebrecon.cgi?v3=1&DB=local&CMD=010a+2006000857&CNT=10+records+per+page|title=Environmental issues: essential primary sources|last1=Lerner|first1=K. Lee|first2=Brenda Wilmoth|date=2006|publisher=Thomson Gale|archive-url=https://archive.today/20120710152134/http://catalog.loc.gov/cgi-bin/Pwebrecon.cgi?v3=1&DB=local&CMD=010a+2006000857&CNT=10+records+per+page|archive-date=10 July 2012|last2=Lerner|access-date=17 November 2016}}</ref> The [[Maunder minimum]], for example, is believed to have caused the [[Little Ice Age]] phenomenon during the [[Middle Ages]].<ref name="future-sun">{{cite web|author=Pogge, Richard W. |date=1997 |url=http://www.astronomy.ohio-state.edu/~pogge/Lectures/vistas97.html |title=The Once & Future Sun |format=lecture notes |work=New Vistas in Astronomy |access-date=3 February 2010 |archive-url=https://web.archive.org/web/20050527094435/http://www-astronomy.mps.ohio-state.edu/Vistas/ |archive-date=27 May 2005 }}</ref>

At the center of the Sun is the core region, a volume of sufficient temperature and pressure for [[nuclear fusion]] to occur. Above the core is the [[radiation zone]], where the plasma conveys the energy flux by means of radiation. Above that is the [[convection zone]] where the gas material transports energy primarily through physical displacement of the gas known as convection. It is believed that the movement of mass within the convection zone creates the magnetic activity that generates sunspots.<ref name="solar FAQ" /> The visible outer surface of the Sun is called the [[photosphere]]. Above this layer is a thin region known as the [[chromosphere]]. This is surrounded by a transition region of rapidly increasing temperatures, and finally by the super-heated [[solar corona|corona]].<ref name=":0" />{{Rp|pages=498–502}}

A solar wind of plasma particles constantly streams outward from the Sun until, at the outermost limit of the Solar System, it reaches the [[heliopause (astronomy)|heliopause]]. As the solar wind passes the Earth, it interacts with the [[Earth's magnetic field]] ([[magnetosphere]]) and deflects the solar wind, but traps some creating the [[Van Allen radiation belt]]s that envelop the Earth. The [[aurora (astronomy)|aurora]] are created when solar wind particles are guided by the magnetic flux lines into the Earth's polar regions where the lines then descend into the [[Earth's atmosphere|atmosphere]].<ref>{{cite web|author = Stern, D.P.|author2 = Peredo, M.|date = 28 September 2004|url=http://www-istp.gsfc.nasa.gov/Education/Intro.html|title = The Exploration of the Earth's Magnetosphere|publisher = NASA|access-date =22 August 2006| archive-url= https://web.archive.org/web/20060824003619/http://www-istp.gsfc.nasa.gov/Education/Intro.html| archive-date= 24 August 2006 | url-status= live}}</ref>