List of solar cycles

Solar cycles are nearly periodic 11-year changes in the Sun's activity that are based on the number of sunspots present on the Sun's surface. The first solar cycle conventionally is said to have started in 1755. 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 remains not fully confirmed.

Solar cycles can be reconstructed indirectly, using the radiocarbon ¹⁴C proxy, for the last millennium.^[5]

The smoothing is done using the traditional SIDC smoothing algorithm.^[6] 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,^[7] with related solar cycles characteristics available in this STCE news item.^[8]

The start of solar cycle 25 was declared by SIDC on September 15, 2020 as being in December 2019.^[9] This makes cycle 24 the only "11-year solar cycle" to have lasted precisely 11 years.

Details of cycles 1 to 25

Solar cycle	Start (Min) (Y-M)	Min SSN (start of cycle)	Max (Y-M)	Max SSN	Ave spots per day	Time of Rise (Y-M)	Length (Y-M)
Solar cycle 1	1755 – Feb	14.0	1761 – Jun	144	(70)	6-4	11-4
Solar cycle 2	1766 – Jun	18.6	1769 – Sep	193	(99)	3-3	9-0
Solar cycle 3	1775 – Jun	12.0	1778 – May	264	(111)	2-11	9-3
Solar cycle 4	1784 – Sep	15.9	1788 – Feb	235	(103)	3-5	13-7
Solar cycle 5	1798 – Apr	5.3	1805 – Feb	82	(38)	6-10	12-3
Solar cycle 6	1810 – Jul	0.0	1816 – May	81	(31)	5-10	12-10
Solar cycle 7	1823 – May	0.1	1829 – Nov	119	(63)	6-6	10-6
Solar cycle 8	1833 – Nov	12.2	1837 – Mar	245	(112)	3-4	9-8
Solar cycle 9	1843 – Jul	17.6	1848 – Feb	220	(99)	4-7	12-5
Solar cycle 10	1855 – Dec	6.0	1860 – Feb	186	92	4-2	11-3
Solar cycle 11	1867 – Mar	9.9	1870 – Aug	234	89	3-5	11-9
Solar cycle 12	1878 – Dec	3.7	1883 – Dec	124	57	5-0	11-3
Solar cycle 13	1890 – Mar	8.3	1894 – Jan	147	65	3-10	11-10
Solar cycle 14	1902 – Jan	4.5	1906 – Feb	107	54	4-1	11-6
Solar cycle 15	1913 – Jul	2.5	1917 – Aug	176	73	4-1	10-1
Solar cycle 16	1923 – Aug	9.3	1928 – Apr	130	68	4-8	10-1
Solar cycle 17	1933 – Sep	5.8	1937 – Apr	199	96	3-7	10-5
Solar cycle 18	1944 – Feb	12.9	1947 – May	219	109	3-3	10-2
Solar cycle 19	1954 – Apr	5.1	1958 – Mar	285	129	3-11	10-6
Solar cycle 20	1964 – Oct	14.3	1968 – Nov	157	86	4-1	11-5
Solar cycle 21	1976 – Mar	17.8	1979 – Dec	233	111	3-9	10-6
Solar cycle 22	1986 – Sep	13.5	1989 – Nov	213	106	3-2	9-11
Solar cycle 23	1996 – Aug	11.2	2001 – Nov	180	82	5-3	12-4
Solar cycle 24	2008 – Dec	2.2	2014 – Apr	116	49	5-4	11-0
Solar cycle 25	2019 – Dec	1.8	2024 – Oct	161	Progr: SC25 (84) SC24 (63)	4–10
Average		9.0		178.7		4.4	11.04

• Notes on Solar cycle 25
  • The maximum SSN of 160.9 for October 2024 is 73% above the maximum SSN predicted by Zharkova for SC25.
  • SILSO has announced October 2024 as the peak of the cycle. It says: "For the coming years, another maximum remains a possibility, but it is unlikely it will be higher than the one in October last year because the Sun has completed its polar field reversal in 2023, and because the ongoing solar cycle is already 5.5 years in progress."
  • The precise final figure for this peak won't be known until October 2025, due to the month of Apr 2025 not yet being finalised.

Unofficial cycles starting with a maximum

The following table is instead divided into (unofficial) cycles starting and ending with a maximum, for the purpose of indicating the number of spotless days associated with each minimum. It begins with cycle 10-11 due to the significant amount of missing daily data before this time, which allows estimated averages to be calculated, but does not permit totals to be counted.

Solar Cycles	Start (Maximum)	Spotless days[10]
Solar cycle 10–11	1860 – Feb	406
Solar cycle 11–12	1870 – Aug	1028
Solar cycle 12–13	1883 – Dec	736
Solar cycle 13–14	1894 – Jan	934
Solar cycle 14–15	1906 – Feb	1023
Solar cycle 15–16	1917 – Aug	534
Solar cycle 16–17	1928 – Apr	568
Solar cycle 17–18	1937 – Apr	269
Solar cycle 18–19	1947 – May	446
Solar cycle 19–20	1958 – Mar	227
Solar cycle 20–21	1968 – Nov	272
Solar cycle 21–22	1979 – Dec	273
Solar cycle 22–23	1989 – Oct	309
Solar cycle 23–24	2001 – Nov	817
Solar cycle 24–25	2014 – Apr	849
Solar cycle 25–26	2024 – Oct	0

Comparison of cycles 24 and 25 by 13-month running averages

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 (Aug 1, 2025) and six months after the end of the month in question.

The table shows averages for each hemisphere and the average for the entire Sun.

Solar Cycle 24					Solar Cycle 25
	North	South	Total		Total	South	North
Dec 2008	1.4	0.8	2.2		1.8	0.9	0.9	Dec 2019
Jan 2009	1.6	0.9	2.5		2.2	1.3	0.9	Jan 2020
Feb 2009	1.6	1.1	2.7		2.7	1.5	1.2	Feb 2020
Mar 2009	1.7	1.2	2.9		3.0	1.5	1.5	Mar 2020
Apr 2009	2.1	1.2	3.3		3.6	2.1	1.5	Apr 2020
May 2009	2.3	1.2	3.5		5.6	3.9	1.6	May 2020
Jun 2009	2.7	1.4	4.1		7.9	6.1	1.8	Jun 2020
Jul 2009	3.6	1.9	5.5		9.0	7.3	1.7	Jul 2020
Aug 2009	4.9	2.5	7.4		9.5	7.6	1.9	Aug 2020
Sep 2009	6.5	3.0	9.5		10	7.9	2.5	Sep 2020
Oct 2009	7.3	3.3	11		12	8.9	3.0	Oct 2020
Nov 2009	8.1	3.6	12		14	9.8	3.8	Nov 2020
Dec 2009	8.4	4.3	13		15	10	5.1	Dec 2020
Jan 2010	9.0	5.0	14		17	11	6.3	Jan 2021
Feb 2010	10	5.6	16		19	12	7.2	Feb 2021
Mar 2010	12	6.4	19		22	14	8.0	Mar 2021
Apr 2010	13	7.4	21		25	16	9.2	Apr 2021
May 2010	15	8.4	23		26	15	10	May 2021
Jun 2010	16	8.8	25		28	16	12	Jun 2021
Jul 2010	17	8.7	25		31	18	13	Jul 2021
Aug 2010	17	9.3	26		35	20	16	Aug 2021
Sep 2010	19	10	29		40	22	18	Sep 2021
Oct 2010	23	12	34		45	24	21	Oct 2021
Nov 2010	26	13	39		51	27	24	Nov 2021
Dec 2010	28	14	42		56	30	26	Dec 2021
Jan 2011	31	15	46		60	32	28	Jan 2022
Feb 2011	34	15	49		65	35	30	Feb 2022
Mar 2011	38	16	54		69	37	31	Mar 2022
Apr 2011	44	17	61		73	39	34	Apr 2022
May 2011	50	20	69		77	39	38	May 2022
Jun 2011	54	23	77		81	40	42	Jun 2022
Jul 2011	58	26	84		87	41	46	Jul 2022
Aug 2011	60	26	86		93	43	49	Aug 2022
Sep 2011	60	27	87		97	46	51	Sep 2022
Oct 2011	59	28	87		99	48	51	Oct 2022
Nov 2011	59	30	89		101	49	53	Nov 2022
Dec 2011	60	33	92		107	50	56	Dec 2022
Jan 2012	59	36	95		113	54	59	Jan 2023
Feb 2012	58	41	98		118	55	62	Feb 2023
Mar 2012	55	43	98		121	54	67	Mar 2023
Apr 2012	51	44	95		123	54	69	Apr 2023
May 2012	47	44	91		124	56	68	May 2023
Jun 2012	45	42	87		125	58	68	Jun 2023
Jul 2012	44	40	84		125	58	67	Jul 2023
Aug 2012	44	41	85		124	58	66	Aug 2023
Sep 2012	44	41	85		124	59	65	Sep 2023
Oct 2012	45	41	86		125	59	66	Oct 2023
Nov 2012	46	42	88		128	61	67	Nov 2023
Dec 2012	45	43	88		129	65	65	Dec 2023
Jan 2013	45	42	87		131	68	63	Jan 2024
Feb 2013	44	42	86		137	75	62	Feb 2024
Mar 2013	43	42	84		141	82	60	Mar 2024
Apr 2013	42	42	84		144	88	57	Apr 2024
May 2013	41	46	87		149	94	55	May 2024
Jun 2013	39	52	91		153	99	54	Jun 2024
Jul 2013	37	58	95		155	102	53	Jul 2024
Aug 2013	35	64	99		157	102	55	Aug 2024
Sep 2013	35	70	105		159	102	57	Sep 2024
Oct 2013	34	73	107		161	103	58	Oct 2024
Nov 2013	32	74	107		157	101	56	Nov 2024
Dec 2013	32	76	108		151	95	56	Dec 2024
Jan 2014	33	76	109		146	90	57	Jan 2025
Feb 2014	35	76	111	(135)			Feb 2025
Mar 2014	36	78	114	(120)			Mar 2025
Apr 2014	36	80	116	(107)			Apr 2025

Comparison of cycles 24 and 25 by daily spots

The following table gives the number of days so far in cycle 25 against the number up to the same point in cycle 24, which have passed various thresholds for the numbers of sunspots.

Counts	SC 24 to Aug 1, 2014	SC 25 to Aug 1, 2025
≥100	551	865
≥125	293	607
≥150	107	373
≥175	25	189
≥200	3	96
≥225	0	36
≥250	0	16
≥275	0	5

As at Aug 1, 2025, solar cycle 25 is averaging 33% more spots per day than solar cycle 24 at the same point in the cycle (Aug 1, 2014).

• Year 1 of SC25 (Dec 2019 to Nov 2020) averaged 101% more spots per day than year 1 of SC24.
• Year 2 of SC25 (Dec 2020 to Nov 2021) averaged 7% more spots per day than year 2 of SC24.
• Year 3 of SC25 (Dec 2021 to Nov 2022) averaged 8% more spots per day than year 3 of SC24.
• Year 4 of SC25 (Dec 2022 to Nov 2023) averaged 41% more spots per day than year 4 of SC24.
• Year 5 of SC25 (Dec 2023 to Nov 2024) averaged 71% more spots per day than year 5 of SC24.
• Year 6 of SC25 (1 Dec 2024 to 1 Aug 2025) is currently averaging 6% more spots per day than at the same point in year 6 of SC24.