Editing Solar cycle (section)

== Cycle history ==
[[File:Sunspots 11000 years.svg|thumb|upright=1.5|Reconstruction of solar activity over 11,400&nbsp;years]]
Sunspot numbers over the past 11,400&nbsp;years have been reconstructed using [[carbon-14]] and [[beryllium-10]] isotope ratios.<ref name="Wu2018">{{Cite journal |first1=C.J. |last1=Wu|first2=N. |last2=Krivova| first3= S.K.|last3= Solanki|first4= I.G.|last4= Usoskin| title=Solar total and spectral irradiance reconstruction over the last 9000 years| journal=Astronomy & Astrophysics |volume=620 |pages=A120 |year=2018 |doi=10.1051/0004-6361/201832956|arxiv=1811.03464|bibcode=2018A&A...620A.120W }}</ref> The level of solar activity beginning in the 1940s is exceptional – the last period of similar magnitude occurred around 9,000&nbsp;years ago (during the warm [[Boreal (period)|Boreal period]]).<ref name="Usoskin07" /><ref name="Solanski2004">{{Cite journal |first1=Sami K. |last1=Solanki |author-link=Sami Solanki |first2=Ilya G. |last2=Usoskin |first3=Bernd |last3=Kromer |first4=Manfred |last4=Schüssler |first5=Jürg |last5=Beer |title=Unusual activity of the Sun during recent decades compared to the previous 11,000&nbsp;years |journal=Nature |volume=431 |year=2004 |pages=1084–1087 |url=http://cc.oulu.fi/%7Eusoskin/personal/nature02995.pdf |doi=10.1038/nature02995 |access-date=17 April 2007 |pmid=15510145 |issue=7012 |bibcode=2004Natur.431.1084S |s2cid=4373732 }}, {{cite web |title=11,000&nbsp;Year Sunspot Number Reconstruction |work=Global Change Master Directory |url=http://gcmd.nasa.gov/KeywordSearch/Metadata.do?Portal=GCMD&KeywordPath=%5BParameters%3ACategory%3D%27EARTH+SCIENCE%27%2CTopic%3D%27SUN-EARTH+INTERACTIONS%27%2CTerm%3D%27SOLAR+ACTIVITY%27%2CVariable%3D%27SUNSPOTS%27%5D&OrigMetadataNode=GCMD&EntryId=NOAA_NCDC_PALEO_2005-015&MetadataView=Brief&MetadataType=0&lbnode=gcmd3b |access-date=2005-03-11 |archive-date=2015-11-02 |archive-url=https://web.archive.org/web/20151102112535/http://gcmd.nasa.gov/KeywordSearch/Metadata.do?Portal=GCMD&KeywordPath=%5BParameters%3ACategory%3D%27EARTH+SCIENCE%27%2CTopic%3D%27SUN-EARTH+INTERACTIONS%27%2CTerm%3D%27SOLAR+ACTIVITY%27%2CVariable%3D%27SUNSPOTS%27%5D&OrigMetadataNode=GCMD&EntryId=NOAA_NCDC_PALEO_2005-015&MetadataView=Brief&MetadataType=0&lbnode=gcmd3b }}</ref><ref>{{Cite journal |first1=Ilya G. |last1=Usoskin | author-link=Ilya G. Usoskin| first2=Sami K. |last2=Solanki |first3=Manfred |last3=Schüssler |first4=Kalevi |last4=Mursula |first5=Katja  |last5= Alanko |author2-link=Sami Solanki |title=A Millennium Scale Sunspot Number Reconstruction: Evidence For an Unusually Active Sun Since the 1940s |journal=[[Physical Review Letters]] |volume=91 |year=2003 |arxiv=astro-ph/0310823 |issue=21 |doi=10.1103/PhysRevLett.91.211101 |pmid=14683287 |page=211101 |bibcode=2003PhRvL..91u1101U
|s2cid=20754479 }}</ref> The Sun was at a similarly high level of magnetic activity for only ~10% of the past 11,400&nbsp;years. Almost all earlier high-activity periods were shorter than the present episode.<ref name="Solanski2004" /> Fossil records suggest that the solar cycle has been stable for at least the last 700&nbsp;million years. For example, the cycle length during the [[Cisuralian|Early Permian]] is estimated to be 10.62&nbsp;years<ref name=Luthardt2017>{{cite journal |first1=Ludwig |last1=Luthardt |first2=Ronny |last2=Rößler |title=Fossil forest reveals sunspot activity in the early Permian |journal=[[Geology (journal)|Geology]] |date=February 2017 |volume=45 |issue=2 |page=279 |doi=10.1130/G38669.1 |bibcode = 2017Geo....45..279L |s2cid=132999292 }}</ref> and similarly in the [[Neoproterozoic]].<ref name=NeoP>{{cite journal |last1=Li |first1=Pengbo |display-authors=etal |title=Sunspot cycles recorded in siliciclastic biolaminites at the dawn of the Neoproterozoic Sturtian glaciation in South China |journal=Precambrian Research |volume=315 |pages=75–91 |date=Sep 2018 |doi=10.1016/j.precamres.2018.07.018|bibcode=2018PreR..315...75L |s2cid=135344975 }}</ref><ref>{{cite journal |last1=Michael Marshall |title=Rock layers show our sun has been in same cycle for 700 million years |journal=New Scientist |date=Aug 18, 2018 |url=https://www.newscientist.com/article/mg23931914-300-rock-layers-show-our-sun-has-been-in-same-cycle-for-700-million-years}}</ref>

[[File:Carbon14 with activity labels.svg|thumb|upright=1.5|Solar activity events recorded in radiocarbon. Present period is on right. Values since 1900 not shown.]]

{| class="wikitable"
|+ Major events and approximate dates
! Event
! Start
! End
|-
| [[Homeric Minimum|Homeric minimum]]<ref name="SedimentStudy">{{cite journal |title=Regional atmospheric circulation shifts induced by a grand solar minimum |journal=[[Nature Geoscience]] |date=2 April 2012 |author1=Celia Martin-Puertas |author2=Katja Matthes |author3=Achim Brauer |author4=Raimund Muscheler |author5=Felicitas Hansen |author6=Christof Petrick |author7=Ala Aldahan |author8=Göran Possnert |author9=Bas van Geel |volume=5 |pages=397–401 |doi=10.1038/ngeo1460 |issue=6 |bibcode=2012NatGe...5..397M}}</ref>
| 750&nbsp;BC
| 550&nbsp;BC
|-
| Oort minimum
| AD 1040
| AD 1080
|-
| Medieval maximum
| 1100
| 1250
|-
|  Wolf minimum
| 1280
| 1350
|-
| [[Spörer Minimum]]
| 1450
| 1550
|-
| [[Maunder Minimum]]
| 1645
| 1715
|-
| [[Dalton Minimum]]
| 1790
| 1820
|-
| [[Modern Maximum]]
| 1933
| 2008
|-
|}

Until 2009, it was thought that 28&nbsp;cycles had spanned the 309&nbsp;years between 1699 and 2008, giving an average length of 11.04&nbsp;years, but research then showed that the longest of these (1784–1799) may actually have been two cycles.<ref>{{Cite journal |first1=I. G. |last1=Usoskin | author-link=Ilya G. Usoskin|first2=K. |last2=Mursula |first3=R. |last3=Arlt |first4=G. A. |last4=Kovaltsov |title=A solar cycle lost in 1793–1800: Early sunspot observations resolve the old mystery |journal=The Astrophysical Journal |volume=700 |issue=2 |pages=L154 |year=2009 |doi=10.1088/0004-637X/700/2/L154 |bibcode=2009ApJ...700L.154U |arxiv=0907.0063|s2cid=14882350 }}</ref><ref>{{cite news |title=Centuries-old sketches solve sunspot mystery |newspaper=New Scientist |page=10 |date=1 Aug 2009 |url=https://www.newscientist.com/article/mg20327194.400}}</ref> If so then the average length would be only around 10.7&nbsp;years. Since observations began cycles as short as 9&nbsp;years and as long as 14&nbsp;years have been observed, and if the cycle of 1784–1799 is double then one of the two component cycles had to be less than 8&nbsp;years in length. Significant amplitude variations also occur.

Several lists of proposed historical "grand minima" of solar activity exist.<ref name="Usoskin07">{{Cite journal |first1=Ilya G. |last1=Usoskin | author-link=Ilya G. Usoskin|first2=Sami K. |last2=Solanki |first3=Gennady A. |last3=Kovaltsov |title=Grand minima and maxima of solar activity: New observational constraints |journal=Astron. Astrophys. |volume=471 |issue=1 |pages=301–309 |url=http://cc.oulu.fi/~usoskin/personal/aa7704-07.pdf |doi=10.1051/0004-6361:20077704 |year=2007 |bibcode=2007A&A...471..301U |arxiv=0706.0385|s2cid=7742132 }}</ref><ref>{{Cite journal|last1=Brauer|first1=Achim|last2=Possnert|first2=Göran|last3=Aldahan|first3=Ala|last4=Błaszkiewicz|first4=Mirosław|last5=Słowinski|first5=Michał|last6=Ott|first6=Florian|last7=Dräger|first7=Nadine|last8=Mekhaldi|first8=Florian|last9=Adolphi|first9=Florian|date=2018-05-31|title=Synchronizing 10Be in two varved lake sediment records to IntCal13 14C during three grand solar minima|journal=Climate of the Past|language=en|volume=14|issue=5|pages=687–696|doi=10.5194/cp-14-687-2018|issn=1814-9324|bibcode=2018CliPa..14..687C|doi-access=free|hdl=21.11116/0000-0003-2C5D-5|hdl-access=free}}</ref>

=== Recent cycles ===

==== Cycle 25 ====
{{Main|Solar cycle 25}}

Solar cycle 25 began in December 2019.<ref name="Hello 25">{{cite web|url=https://www.weather.gov/news/201509-solar-cycle|title=Hello Solar Cycle 25|author=[[National Weather Service]]|access-date=15 September 2020}}</ref> Several predictions have been made for solar cycle 25<ref name="ADS serach">for example: {{cite web |title=ADS search for "solar sunspot cycle 25 prediction" |url=https://ui.adsabs.harvard.edu/search/q=abs%3A(prediction%20solar%20sunspot%20%22cycle%2025%22)&sort=date%20desc%2C%20bibcode%20desc&p_=0 |access-date= 17 March 2020}}</ref> based on different methods, ranging from very weak to strong magnitude. A physics-based prediction relying on the data-driven solar dynamo and solar surface flux transport models seems to have predicted the strength of the solar polar field at the current minima correctly and forecasts a weak but not insignificant solar cycle 25 similar to or slightly stronger than cycle 24.<ref name=Bhowmik>{{cite journal |last1=Bhowmik |first1=Prantika |last2=Nandy |first2=Dibyendu |title=Prediction of the strength and timing of sunspot cycle 25 reveal decadal-scale space environmental conditions |journal=Nature Communications |date=6 December 2018 |volume=9 |issue=1 |page=5209 |doi=10.1038/s41467-018-07690-0 |pmid=30523260 |pmc=6283837 |arxiv=1909.04537 |bibcode=2018NatCo...9.5209B |language=en |issn=2041-1723|doi-access=free }}</ref> Notably, they rule out the possibility of the Sun falling into a Maunder-minimum-like (inactive) state over the next decade. A preliminary consensus by a solar cycle 25 Prediction Panel was made in early 2019.<ref>{{Cite web |url=https://www.swpc.noaa.gov/news/solar-cycle-25-preliminary-forecast|title=Solar Cycle 25 Preliminary Forecast |website=NOAA / NWS Space Weather Prediction Center}}</ref> The Panel, which was organized by NOAA's [[Space Weather Prediction Center]] (SWPC) and [[NASA]], based on the published solar cycle 25 predictions, concluded that solar cycle 25 will be very similar to solar cycle 24. They anticipate that the solar cycle minimum before cycle 25 will be long and deep, just as the minimum that preceded cycle 24. They expect solar maximum to occur between 2023 and 2026 with a sunspot range of 95 to 130, given in terms of the revised sunspot number.

==== Cycle 24 ====
{{Main|Solar cycle 24}}
Solar cycle 24 began on 4&nbsp;January 2008,<ref>{{Cite press release | author1=  Bernhard Fleck | date= 14 January 2008 |url=http://www.esa.int/Our_Activities/Space_Science/SOHO_the_new_solar_cycle_starts_with_a_bang |title=SOHO: the new solar cycle starts with a 'bang' |work=European Space Agency |access-date=2017-05-11 |language=en-GB}}</ref> with minimal activity until early 2010.<ref>{{Cite news |title=Solar Cycle&nbsp;24 begins |date=2008-01-10 |author=Tony Phillips |url=https://science.nasa.gov/science-news/science-at-nasa/2008/10jan_solarcycle24/ |work=NASA |access-date=2010-05-29 |archive-date=2021-02-28 |archive-url=https://web.archive.org/web/20210228054909/https://science.nasa.gov/science-news/science-at-nasa/2008/10jan_solarcycle24/ }}</ref><ref>{{Cite news |title=As the Sun Awakens, NASA Keeps a Wary Eye on Space Weather |date=2010-06-04 |author=Tony Phillips |url=https://science.nasa.gov/science-news/science-at-nasa/2010/04jun_swef/ |work=NASA |access-date=2013-05-18 |archive-date=2021-03-20 |archive-url=https://web.archive.org/web/20210320221857/https://science.nasa.gov/science-news/science-at-nasa/2010/04jun_swef }}</ref> The cycle featured a "double-peaked" [[solar maximum]]. The first peak reached 99 in 2011 and the second in early 2014 at 101.<ref>{{cite web |title=Solar Cycle Progression |website=NOAA / NWS Space Weather Prediction Center |url=http://www.swpc.noaa.gov/products/solar-cycle-progression |access-date=2015-07-06}}</ref> Cycle&nbsp;24 ended in December 2019 after 11.0 years.<ref name="Hello 25" />

==== Cycle 23 ====
{{Main|Solar cycle 23}}
Solar cycle 23 lasted 11.6&nbsp;years, beginning in May&nbsp;1996 and ending in January&nbsp;2008. The maximum smoothed sunspot number (monthly number of sunspots averaged over a twelve-month period) observed during the solar cycle was 120.8 (March&nbsp;2000), and the minimum was 1.7.<ref name="SIDC Monthly Smoothed Sunspot Number">{{Cite web|url=http://www.sidc.be/silso/datafiles|title=Sunspot Number &#124; SILSO |website=www.sidc.be}}</ref> A total of 805&nbsp;days had no sunspots during this cycle.<ref name="Spotless Days">{{cite web |title=Spotless Days |url=http://spaceweather.com/glossary/spotlessdays.htm?PHPSESSID=dli444kmrjgre0rjq6l86fv144}}</ref><ref name="What's Wrong with the Sun? (Nothing)">{{cite web |title=What's wrong with the Sun? (Nothing) more information: Spotless Days |url=https://science.nasa.gov/headlines/y2008/11jul_solarcycleupdate.htm |archive-url=https://web.archive.org/web/20080714032353/https://science.nasa.gov/headlines/y2008/11jul_solarcycleupdate.htm |archive-date=2008-07-14}}</ref><ref name="Solaemon's Spotless Days Page">{{cite web |title=Solaemon's Spotless Days Page |url=http://users.telenet.be/j.janssens/Spotless/Spotless.html |access-date=2015-08-15 |archive-date=2017-07-22 |archive-url=https://web.archive.org/web/20170722234836/http://users.telenet.be/j.janssens/Spotless/Spotless.html }}</ref>