Editing Solar flare (section)

=== Soft X-ray ===
[[File:GOES-16 X-ray flux (1-minute data) on 2023-12-14 with flares labeled.svg|thumb|upright=1.6|An M5.8, M2.3, and X2.8 flare were recorded by [[GOES-16]] on 14 December 2023. Their corresponding peak fluxes in the 0.1 to 0.8&nbsp;nm channel were 5.8×10<sup>−5</sup>, 2.3×10<sup>−5</sup>, and 2.8×10<sup>−4</sup> W/m<sup>2</sup>, respectively.]]
The modern classification system for solar flares uses the letters A, B, C, M, or X, according to the peak [[flux]] in watts per square metre (W/m<sup>2</sup>) of [[soft X-ray]]s with [[wavelength]]s {{convert|0.1|to|0.8|nm|angstrom|abbr=off|lk=on|sigfig=1}}, as measured by [[GOES]] satellites in [[geosynchronous orbit]].

{| class="wikitable"
|-
! Classification !! Peak flux range (W/m<sup>2</sup>)
|-
| A || < 10<sup>−7</sup>
|-
| B || 10<sup>−7</sup> – 10<sup>−6</sup>
|-
| C || 10<sup>−6</sup> – 10<sup>−5</sup>
|-
| M || 10<sup>−5</sup> – 10<sup>−4</sup>
|-
| X || > 10<sup>−4</sup>
|}

The strength of an event within a class is noted by a numerical suffix ranging from 1 up to, but excluding, 10, which is also the factor for that event within the class. Hence, an X2 flare is twice the strength of an X1 flare, an X3 flare is three times as powerful as an X1. M-class flares are a tenth the size of X-class flares with the same numeric suffix.<ref>{{cite web|url=http://www.nasa.gov/feature/goddard/2017/active-region-on-sun-continues-to-emit-solar-flares|title=Sun Erupts With Significant Flare|first=Rob|last=Garner|date=6 September 2017|website=NASA|access-date=2 June 2019}}</ref> An X2 is four times more powerful than an M5 flare.<ref>{{citation |title=Heliophysics: Space Storms and Radiation: Causes and Effects |page=375 |year=2010 |editor1-last=Schrijver |editor1-first=Carolus J. |url=https://books.google.com/books?id=OukfAwAAQBAJ&pg=PA375 |publisher=Cambridge University Press |isbn=978-1107049048 |editor2-last=Siscoe |editor2-first=George L. |editor2-link=George Siscoe}}.</ref> X-class flares with a peak flux that exceeds 10<sup>−3</sup> W/m<sup>2</sup> may be noted with a numerical suffix equal to or greater than 10.

This system was originally devised in 1970 and included only the letters C, M, and X. These letters were chosen to avoid confusion with other optical classification systems. The A and B classes were added in the 1990s as instruments became more sensitive to weaker flares. Around the same time, the [[backronym]] ''moderate'' for M-class flares and ''extreme'' for X-class flares began to be used.<ref name="pietrow22">{{cite thesis |type=PhD |last=Pietrow |first=A. G. M. |date=2022 |title=Physical properties of chromospheric features: Plage, peacock jets, and calibrating it all. |publisher=Stockholm University |url=https://www.diva-portal.org/smash/record.jsf?aq2=%5B%5B%5D%5D&c=10&af=%5B%5D&searchType=LIST_LATEST&sortOrder2=title_sort_asc&query=&language=en&pid=diva2%3A1651858&aq=%5B%5B%5D%5D&sf=all&aqe=%5B%5D&sortOrder=author_sort_asc&onlyFullText=false&noOfRows=50&dswid=5451 |doi=10.13140/RG.2.2.36047.76968 |doi-access=free |place=Stockholm, Sweden}}</ref>