Editing Solar flare (section)

== Observational history<span class="anchor" id="Observations"></span><span class="anchor" id="History"></span> ==
{{Further|Solar observation}}
Flares produce radiation across the electromagnetic spectrum, although with different intensity. They are not very intense in visible light, but they can be very bright at particular [[spectral line]]s. They normally produce [[bremsstrahlung]] in X-rays and [[synchrotron radiation]] in radio.<ref>{{Cite journal |last=Winckler |first=J. R. |date=1964-01-01 |title=Energetic X-Ray Bursts From Solar Flares |url=https://ui.adsabs.harvard.edu/abs/1964NASSP..50..117W |journal=NASA Special Publication |volume=50 |pages=117|bibcode=1964NASSP..50..117W }}</ref>

=== Optical observations ===
[[File:Carrington Richard drawing of 1859 sunspots.jpeg|thumb|Richard Carrington's sketch of the first recorded solar flare (A and B mark the initial bright points which moved over the course of five minutes to C and D before disappearing.)<ref name="Carrington1859">{{cite journal |last1=Carrington |first1=R. C. |date=November 1859 |title=Description of a Singular Appearance seen in the Sun on September 1, 1859 |url=https://academic.oup.com/mnras/article/20/1/13/983482 |journal=Monthly Notices of the Royal Astronomical Society |volume=20 |pages=13–15 |bibcode=1859MNRAS..20...13C |doi=10.1093/mnras/20.1.13 |bibcode-access=free |doi-access=free}}</ref>]]
Solar flares were first observed by [[Richard Christopher Carrington|Richard Carrington]] and [[Richard Hodgson (publisher)|Richard Hodgson]] independently on [[Solar storm of 1859|1 September 1859]] by projecting the image of the solar disk produced by an optical telescope through a broad-band filter.<ref name=":0">{{cite journal |last=Carrington |first=Richard C. |date=November 1859 |title=Description of a singular appearance seen in the Sun on September&nbsp;1, 1859 |url=https://babel.hathitrust.org/cgi/pt?id=njp.32101081655332&view=1up&seq=357 |journal=Monthly Notices of the Royal Astronomical Society |volume=20 |issue=1 |pages=13–15 |bibcode=1859MNRAS..20...13C |doi=10.1093/mnras/20.1.13 |doi-access=free}}</ref><ref>{{cite journal |last1=Hodgson |first1=Richard |date=November 1859 |title=On a curious Appearance seen in the Sun |url=https://babel.hathitrust.org/cgi/pt?id=njp.32101081655332&view=1up&seq=359 |journal=Monthly Notices of the Royal Astronomical Society |volume=20 |issue=1 |pages=15–16|doi=10.1093/mnras/20.1.15a |doi-access=free }}</ref> It was an extraordinarily intense ''white light flare'', a flare emitting a high amount of light in the [[visual spectrum]].<ref name=":0" />

Since flares produce copious amounts of radiation at [[H-alpha]],<ref>{{Cite journal |last1=Druett |first1=Malcolm |last2=Scullion |first2=Eamon |last3=Zharkova |first3=Valentina |last4=Matthews |first4=Sarah |last5=Zharkov |first5=Sergei |last6=Rouppe Van der Voort |first6=Luc |date=27 June 2017 |title=Beam electrons as a source of Hα flare ribbons |journal=Nature Communications |language=en |volume=8 |issue=1 |page=15905 |bibcode=2017NatCo...815905D |doi=10.1038/ncomms15905 |issn=2041-1723 |pmc=5490266 |pmid=28653670}}</ref> adding a narrow (≈1 Å) passband filter centered at this wavelength to the optical telescope allows the observation of not very bright flares with small telescopes. For years Hα was the main, if not the only, source of information about solar flares. Other passband filters are also used.{{Citation needed|date=June 2024}}

=== Radio observations ===
{{Further|Solar radio emission}}
{{Unreferenced section|date=June 2024}}
During [[World War II]], on February 25 and 26, 1942, British radar operators observed radiation that [[James Stanley Hey|Stanley Hey]] interpreted as solar emission. Their discovery did not go public until the end of the conflict. The same year, [[George Clark Southworth|Southworth]] also observed the Sun in radio, but as with Hey, his observations were only known after 1945. In 1943, [[Grote Reber]] was the first to report radioastronomical observations of the Sun at 160&nbsp;MHz. The fast development of [[radioastronomy]] revealed new peculiarities of the solar activity like ''storms'' and ''bursts'' related to the flares. Today, ground-based radiotelescopes observe the Sun from c. 15&nbsp;MHz up to 400&nbsp;GHz.

=== Space telescopes ===
{{Unreferenced section|date=June 2024}}
[[File:SDO EVE Late Phase Flares.webm|thumb|Observations of a solar flare by different instruments aboard the [[Solar Dynamics Observatory]]]]
Because the Earth's atmosphere [[Absorption (electromagnetic radiation)|absorb]]s much of the electromagnetic radiation emitted by the Sun with wavelengths shorter than 300&nbsp;nm, space-based telescopes allowed for the observation of solar flares in previously unobserved high-energy spectral lines. Since the 1970s, the GOES series of satellites have been continuously observing the Sun in soft X-rays, and their observations have become the standard measure of flares, diminishing the importance of the H-alpha classification. Additionally, space-based telescopes allow for the observation of extremely long wavelengths—as long as a few kilometres—which cannot propagate through the ionosphere.

=== Examples of large solar flares ===
{{See also|List of solar storms#Soft X-ray solar flares}}
[[File:ExtremeEvent 20031026-00h 20031106-24h.jpg|thumb|Space weather conditions, including the soft-X-ray flux (top row), during the [[2003 Halloween solar storms]]<ref>{{cite web | title=Extreme Space Weather Events | publisher=[[National Geophysical Data Center]] | url=http://sxi.ngdc.noaa.gov/sxi_greatest.html | access-date=May 21, 2012 | archive-date=May 22, 2012 | archive-url=https://web.archive.org/web/20120522031032/http://sxi.ngdc.noaa.gov/sxi_greatest.html | url-status=dead }}</ref>]]

The most powerful flare ever observed is thought to be the flare associated with the 1859 Carrington Event.<ref>{{cite web |last1=Bell |first1=Trudy E. |last2=Phillips |first2=Tony |title=A Super Solar Flare |url=https://science.nasa.gov/science-news/science-at-nasa/2008/06may_carringtonflare/ |website=Science News |publisher=NASA Science |access-date=22 December 2012 |archive-url=https://web.archive.org/web/20100412084331/https://science.nasa.gov/science-news/science-at-nasa/2008/06may_carringtonflare/ |archive-date=12 April 2010 |date=6 May 2008 |url-status=dead}}</ref> While no soft X-ray measurements were made at the time, the magnetic crochet associated with the flare was recorded by ground-based magnetometers allowing the flare's strength to be estimated after the event. Using these magnetometer readings, its soft X-ray class has been estimated to be greater than X10<ref>{{cite journal |last1=Cliver |first1=E. W. |last2=Svalgaard |first2=L. |title=The 1859 Solar–Terrestrial Disturbance And the Current Limits of Extreme Space Weather Activity |journal=Solar Physics |date=October 2004 |volume=224 |issue=1–2 |pages=407–422 |doi=10.1007/s11207-005-4980-z |url=https://archive.org/details/DTIC_ADA434906/page/n1/mode/2up |bibcode=2004SoPh..224..407C|s2cid=120093108 }}</ref> and around X45 (±5).<ref>{{cite web |last1=Woods |first1=Tom |title=Solar Flares |url=http://lasp.colorado.edu/media/education/reu/2011/docs/talks/Woods_Flare_Lecture_Jun11.pdf |url-status=live |archive-url=https://web.archive.org/web/20151023060752/http://lasp.colorado.edu/media/education/reu/2011/docs/talks/Woods_Flare_Lecture_Jun11.pdf |archive-date=23 October 2015 |access-date=24 November 2019}}</ref><ref>{{cite journal |last1=Cliver |first1=Edward W. |last2=Dietrich |first2=William F. |title=The 1859 space weather event revisited: limits of extreme activity |url=https://www.swsc-journal.org/articles/swsc/pdf/2013/01/swsc130015.pdf |date=4 April 2013 |journal=J. Space Weather Space Clim. |volume=3 |pages=A31 |doi=10.1051/swsc/2013053 |bibcode=2013JSWSC...3A..31C |access-date=31 December 2023}}</ref>

In modern times, the largest solar flare measured with instruments occurred on [[Halloween solar storms, 2003|4 November 2003]]. This event saturated the GOES detectors, and because of this, its classification is only approximate. Initially, extrapolating the GOES curve, it was estimated to be X28.<ref>{{cite web |title=X-Whatever Flare! (X 28) |url=https://soho.nascom.nasa.gov/hotshots/2003_11_04/ |website=SOHO Hotshots |publisher=ESA/NASA |access-date=21 May 2012 |date=4 November 2003}}</ref> Later analysis of the ionospheric effects suggested increasing this estimate to X45.<ref>{{cite web |url=http://www.spaceref.com/news/viewpr.html?pid=13844 |title=Biggest ever solar flare was even bigger than thought {{!}} SpaceRef – Your Space Reference |date=2004-03-15 |publisher=SpaceRef |access-date=May 21, 2012 |archive-date=2012-09-10 |archive-url=https://archive.today/20120910055509/http://www.spaceref.com/news/viewpr.html?pid=13844 |url-status=dead }}</ref><ref>{{Cite journal |last1=Curto |first1=Juan José |last2=Castell |first2=Josep |last3=Moral |first3=Ferran Del |date=2016 |title=Sfe: waiting for the big one |url=https://www.swsc-journal.org/articles/swsc/abs/2016/01/swsc150071/swsc150071.html |journal=Journal of Space Weather and Space Climate |language=en |volume=6 |pages=A23 |doi=10.1051/swsc/2016018 |bibcode=2016JSWSC...6A..23C |issn=2115-7251|doi-access=free }}</ref> This event produced the first clear evidence of a new spectral component above 100&nbsp;GHz.<ref>{{cite journal |last1=Kaufmann |first1=Pierre |last2=Raulin |first2=Jean-Pierre |last3=de Castro |first3=C. G. Gimnez |last4=Levato |first4=Hugo |last5=Gary |first5=Dale E. |last6=Costa |first6=Joaquim E. R. |last7=Marun |first7=Adolfo |last8=Pereyra |first8=Pablo |last9=Silva |first9=Adriana V. R. |last10=Correia |first10=Emilia |title=A New Solar Burst Spectral Component Emitting Only in the Terahertz Range |journal=The Astrophysical Journal |date=10 March 2004 |volume=603 |issue=2 |pages=L121–L124 |doi=10.1086/383186 |doi-access=free |bibcode=2004ApJ...603L.121K |bibcode-access=free|s2cid=54878789 |s2cid-access=free}}</ref>