List of solar cycles

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The following is a list of solar cycles (sometimes called sunspot cycles), tracked since 1755 following the original numbering proposed by Rudolf Wolf in the mid-19th century. The source data are the revised International Sunspot Numbers (ISN v2.0), as available at SILSO.[1] Sunspot counts exist since 1610[2] but the cycle numbering is not well defined during the Maunder minimum.[3] It was proposed that one cycle might have been lost in the late 18th century,[4] but this still remains not fully confirmed.

The smoothing is done using the traditional SIDC smoothing algorithm.[5] Using this algorithm, if the month in question is notated month 0, a weighted average is formed of months -6 to 6, where months -5 to 5 are given weightings of 1, and months -6 and 6 are given weightings of 0.5. Other smoothing formulas exist, and they usually give slightly different values for the amplitude and timings of the solar cycles. An example is the Meeus smoothing formula,[6] with related solar cycles characteristics available in this STCE news item.[7]

The start of solar cycle 25 was declared by SIDC on September 15 2020 as being in December 2019.[8] This makes cycle 24 the only "11-year solar cycle" to have lasted precisely 11 years.

Solar Cycle Start (Minimum) Smoothed minimum ISN (start of cycle) Maximum Smoothed maximum ISN Average spots per day Time of Rise (years) Duration (years) Spotless days[9][10]
Solar cycle 1 1755-02 14.0 1761-06 144 6.3 11.3
Solar cycle 2 1766-06 18.6 1769-09 193 3.3 9.0
Solar cycle 3 1775-06 12.0 1778-05 264 2.9 9.3
Solar cycle 4 1784-09 15.9 1788-02 235 3.4 13.6
Solar cycle 5 1798-04 5.3 1805-02 82 6.8 12.3
Solar cycle 6 1810-08 0.0 1816-05 81 5.8 12.8
Solar cycle 7 1823-05 0.2 1829-11 119 6.5 10.5
Solar cycle 8 1833-11 12.2 1837-03 245 3.3 9.7
Solar cycle 9 1843-07 17.6 1848-02 220 4.6 12.4
Solar cycle 10 1855-12 6.0 1860-02 186 92 4.2 11.3 561
Solar cycle 11 1867-03 9.9 1870-08 234 89 3.4 11.8 942
Solar cycle 12 1878-12 3.7 1883-12 124 57 5.0 11.3 872
Solar cycle 13 1890-03 8.3 1894-01 147 65 3.8 11.8 782
Solar cycle 14 1902-01 4.5 1906-02 107 54 4.1 11.5 1007
Solar cycle 15 1913-07 2.5 1917-08 176 73 4.1 10.1 640
Solar cycle 16 1923-08 9.4 1928-04 130 68 4.7 10.1 514
Solar cycle 17 1933-09 5.8 1937-04 199 96 3.6 10.4 384
Solar cycle 18 1944-02 12.9 1947-05 219 109 3.3 10.2 382
Solar cycle 19 1954-04 5.1 1958-03 285 129 3.9 10.5 337
Solar cycle 20 1964-10 14.3 1968-11 157 86 4.1 11.4 285
Solar cycle 21 1976-03 17.8 1979-12 233 111 3.8 10.5 283
Solar cycle 22 1986-09 13.5 1989-11 214 106 3.2 9.9 257
Solar cycle 23 1996-08 11.2 2001-11 180 82 5.3 12.3 619
Solar cycle 24 2008-12 2.2 2014-04 116 49 5.3 11.0 914
Solar cycle 25 2019-12 1.8 Progressive: 19.1 (Feb 2021)

[Same point last cycle: 16.1]

266 (Sep 27 2021)

(Same point last cycle: 328)

Average 9.0 178.7 4.4 11.04

The following table is instead divided into (unofficial) cycles starting and ending with a maximum, to give a better feel for the number of spotless days associated with each minimum:

Solar Cycles “Start” (Maximum) Spotless days
Solar cycle 10-11 1860-02 406
Solar cycle 11-12 1870-08 1028
Solar cycle 12-13 1883-12 736
Solar cycle 13-14 1894-01 934
Solar cycle 14-15 1906-02 1023
Solar cycle 15-16 1917-08 534
Solar cycle 16-17 1928-04 568
Solar cycle 17-18 1937-04 269
Solar cycle 18-19 1947-05 446
Solar cycle 19-20 1958-03 227
Solar cycle 20-21 1968-11 272
Solar cycle 21-22 1979-12 273
Solar cycle 22-23 1989-10 309
Solar cycle 23-24 2001-11 817
Solar cycle 24-25 2014-04 842 (Sep 27 2021)

[Same point last cycle: 809]

Following is a comparison of the growth of cycle 25 versus cycle 24, using the 13-month sunspot averages, beginning with the months of the respective minimums.
Numbers in brackets for cycle 25 indicate the minimum possible value for that month, assuming there are no more sunspots between now (27 Sep 2021) and six months after the end of the month in question.

Solar Cycle 24 Solar Cycle 25
Dec 2008 2.2 Dec 2019 1.8
Jan 2009 2.5 Jan 2020 2.2
Feb 2009 2.7 Feb 2020 2.7
Mar 2009 2.9 Mar 2020 3.0
Apr 2009 3.3 Apr 2020 3.6
May 2009 3.5 May 2020 5.6
Jun 2009 4.1 Jun 2020 7.9
Jul 2009 5.5 Jul 2020 9.0
Aug 2009 7.4 Aug 2020 9.5
Sep 2009 9.5 Sep 2020 10.5
Oct 2009 10.9 Oct 2020 11.9
Nov 2009 11.7 Nov 2020 13.6
Dec 2009 12.7 Dec 2020 15.3
Jan 2010 14.0 Jan 2021 17.3
Feb 2010 16.1 Feb 2021 19.1
Mar 2010 18.5 Mar 2021 (22)
Apr 2010 21 Apr 2021 (23)
May 2010 23 May 2021 (21)
Jun 2010 25 Jun 2021 (18.3)
Jul 2010 25 Jul 2021 (16.9)
Aug 2010 26 Aug 2021 (16.1)
Sep 2010 29 Sep 2021 (15.1)
Oct 2010 34 Oct 2021
Nov 2010 39 Nov 2021
Dec 2010 42 Dec 2021
Jan 2011 46 Jan 2022
Feb 2011 49 Feb 2022
Mar 2011 54 Mar 2022
Apr 2011 61 Apr 2022
May 2011 69 May 2022
Jun 2011 77 Jun 2022
Jul 2011 84 Jul 2022
Aug 2011 86 Aug 2022
Sep 2011 87 Sep 2022
Oct 2011 87 Oct 2022
Nov 2011 89 Nov 2022
Dec 2011 92 Dec 2022
Jan 2012 95 Jan 2023
Feb 2012 98 Feb 2023
Mar 2012 98 Mar 2023
Apr 2012 95 Apr 2023
May 2012 91 May 2023
Jun 2012 87 Jun 2023
Jul 2012 84 Jul 2023
Aug 2012 85 Aug 2023
Sep 2012 85 Sep 2023
Oct 2012 86 Oct 2023
Nov 2012 88 Nov 2023
Dec 2012 88 Dec 2023
Jan 2013 87 Jan 2024
Feb 2013 86 Feb 2024
Mar 2013 84 Mar 2024
Apr 2013 84 Apr 2024
May 2013 87 May 2024
Jun 2013 91 Jun 2024
Jul 2013 95 Jul 2024
Aug 2013 99 Aug 2024
Sep 2013 105 Sep 2024
Oct 2013 107 Oct 2024
Nov 2013 107 Nov 2024
Dec 2013 108 Dec 2024
Jan 2014 109 Jan 2025
Feb 2014 111 Feb 2025
Mar 2014 114 Mar 2025
Apr 2014 116 Apr 2025


The following table gives the number of days so far in cycle 25 (to Sep 27 2021), and up to the same point in cycle 24 (to Sep 27 2010), which have passed various thresholds for the numbers of sunspots:

Solar Cycle 24 Solar Cycle 25
≥40 sunspots 35 days 67 days
≥50 16 39
≥60 1 21
≥70 0 16
≥80 0 9
≥90 0 4
≥100 0 0

References[edit]

  1. ^ "Sunspot numbers". WDC-SILSO. Royal Observatory of Belgium. Retrieved 19 May 2017.
  2. ^ Hathaway, D. (2015). "The solar cycle". Living Reviews in Solar Physics. 12 (1): 4. arXiv:1502.07020. Bibcode:2015LRSP...12....4H. doi:10.1007/lrsp-2015-4. PMC 4841188. PMID 27194958.
  3. ^ Usoskin; Mursula; Kovaltsov (2001). "Heliospheric modulation of cosmic rays and solar activity during the Maunder minimum". J. Geophys. Res. 106(A8) (A8): 16039. Bibcode:2001JGR...10616039U. doi:10.1029/2000JA000105.
  4. ^ Usoskin; et al. (2009). "A solar cycle lost in 1793-1800: Early sunspot observations resolve the old mystery". Astrophys. J. Lett. 700 (2): L154. arXiv:0907.0063. Bibcode:2009ApJ...700L.154U. doi:10.1088/0004-637X/700/2/L154. S2CID 14882350.
  5. ^ "SIDC smoothing formula". WDC-SILSO. Royal Observatory of Belgium. Retrieved 19 May 2017.
  6. ^ Meeus, J. (1958). "Une formule d'adoucissement pour l'activité solaire". Ciel et Terre. 74: 445. Bibcode:1958C&T....74..445M.
  7. ^ "The solar cycle's new clothes". STCE. Royal Observatory of Belgium. Retrieved 8 July 2015.
  8. ^ "December 2019 confirmed as starting point of the new solar activity cycle". SIDC.
  9. ^ "What's Wrong with the Sun?". NASA Science. NASA. Retrieved 29 July 2014.
  10. ^ "Spotless Days Page". SILSO. Royal Observatory of Belgium. Retrieved 3 April 2017.

External links[edit]