Sunspot cycle lookup

Key figures

1. The monthly mean sunspot number was 45.7 in October 2026 (provisional), 82 months after the start of Solar Cycle 25. #
2. Solar Cycle 25's highest 13-month smoothed value so far is 160.9, in October 2024. That ranks 15th of the 25 numbered cycles and is 38.2% above Solar Cycle 24's maximum of 116.4 (April 2014). #
3. The strongest cycle on record is Solar Cycle 19, with a smoothed maximum of 285.0 in March 1958. The weakest is Solar Cycle 6, with 81.2 in May 1816. #
4. The highest monthly mean since 1749 is 398.2, in May 1778, during Solar Cycle 3. #
5. The 24 complete cycles (1 to 24) lasted 11.0 years on average, ranging from 9.0 to 13.6 years. #
6. 67 months since 1749 had a monthly mean of zero. 50 of them fell between 1790 and 1830, the period of very low activity known as the Dalton Minimum, and the most recent was August 2009. #

Every solar cycle since 1755

Minimum and maximum dates and values are 13-month smoothed monthly sunspot numbers from the SILSO table of cycle minima and maxima. Each cycle has its own link, for example #cycle-19.

Example: the strongest cycle on record

Solar Cycle 19 began in April 1954, at a smoothed minimum of 5.1, and lasted 126 months (10.5 years), until the next minimum in October 1964. It reached its smoothed maximum of 285.0 in March 1958, 47 months (3.9 years) after the minimum. Its highest monthly mean was 359.4, in October 1957. Compared with Solar Cycle 25's highest smoothed value so far (160.9, October 2024), its maximum was 77.1% higher.

Yearly mean sunspot number since 1749

Each row has its own link, for example #year-1958. The cycle column shows the solar cycle in progress in the middle of each year.

Cite or link to this tool

Teachers, students, writers, radio amateurs and researchers are welcome to use and link to this lookup. Each cycle, year and key figure has its own link, such as #cycle-25, #year-2000 or #strongest-cycle.

How the lookup works

Monthly values are the monthly mean total sunspot number (version 2.0) from the World Data Center SILSO at the Royal Observatory of Belgium, Brussels, which runs from January 1749. Recent months use the same SILSO values as published by the NOAA Space Weather Prediction Center for the Solar Cycle 25 tracker; values from July 2026 onward are provisional and may be revised by SILSO. Yearly means for complete years are SILSO's own yearly mean total sunspot number, which SILSO calculates from daily values, so they can differ by a few tenths from an average of the twelve monthly means. The current year shows the average of the months published so far.

Solar cycle start dates and smoothed minimum and maximum values come from the SILSO table of solar cycle minima and maxima (CSV). Each cycle runs from its smoothed minimum to the month before the next cycle's minimum. The 13-month smoothed value for a month is SILSO's standard running mean over 13 months centred on that month, with the first and last months at half weight; PolarisWire's calculation matches SILSO's published smoothed series to within 0.1. Smoothed values need six months of later data, so the most recent six months have none yet.

Solar Cycle 25 began in December 2019. SILSO has not yet listed an official maximum for it, so the lookup uses its highest smoothed value so far (160.9, October 2024). Comparisons with Cycle 25 line months up by the time since each cycle's minimum. The years 1749 to early 1755 come before Solar Cycle 1, where the numbering of cycles begins. This page is updated daily with the tracker's latest data.