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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. Sunspot counts exist since 1610 but the cycle numbering is not well defined during the Maunder minimum. It was proposed that one cycle might have been lost in the late 18th century, but this remains not fully confirmed.

Solar cycles can be reconstructed indirectly, using the radiocarbon <sup>14</sup>C proxy, for the last millennium.

The smoothing is done using the traditional SIDC smoothing algorithm. 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, with related solar cycles characteristics available in this STCE news item.

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

Details of cycles 1 to 25

  • 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."

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.

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 (Feb 1, 2026) 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.

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.

As at Feb 1, 2026, solar cycle 25 is averaging 30% more spots per day than solar cycle 24 at the same point in the cycle (Feb 1, 2015).

  • 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 (Dec 2024 to Nov 2025) averaged 10% more spots per day than year 6 of SC24.
  • Year 7 of SC25 (1 Dec 2025 to 1 Feb 2026) is averaging 14% more spots per day than at the same point in year 7 of SC24.

References

External links