Sunspot number drops to 45.7 in October, a fifth straight monthly fall and the lowest since 2021
The monthly sunspot number fell to 45.7 in October 2026, the lowest since November 2021 and the fifth monthly drop in a row, a run last seen in 2016.
The story in focus
The Sun's monthly sunspot number fell to 45.7 in October 2026, the lowest reading since November 2021, according to provisional figures from WDC-SILSO at the Royal Observatory of Belgium, shown in the PolarisWire Solar Cycle 25 tracker. It was the fifth monthly decline in a row, the first run of that length since 2016, and leaves activity about 79% below the cycle's August 2024 peak.
- The monthly mean international sunspot number was 45.7 in October 2026 (provisional), down from 60.3 in September and 114.8 in October 2025, and the lowest since 34.8 in November 2021.
- October was the fifth monthly fall in a row (101.8 in May, then 93.3, 78.1, 76.0, 60.3 and 45.7), the first run of five or more consecutive monthly declines since the one that ended in April 2016.
- The average for August to October 2026 was 60.7, the lowest three-month average since the three months to January 2022; the 12-month average to October was 85.8, against 131.2 a year earlier.
- Solar Cycle 25's highest month was August 2024 at 216.0; October 2026 is about 79% below that. The 13-month smoothed number, which peaked at 160.9 in October 2024, was 88.6 in April 2026, the lowest since July 2022.
What the latest data show
The international sunspot number, compiled by the World Data Center SILSO at the Royal Observatory of Belgium, averaged 45.7 in October 2026. That is down 24% from 60.3 in September and 60% from 114.8 in October 2025. No month has had a lower value since November 2021, when the figure was 34.8, early in the rising phase of Solar Cycle 25. SILSO lists all 2026 monthly values as provisional, so the figure can still be revised slightly.
October's reading continues a steady slide through the second half of the year. The monthly number was 101.8 in May, 93.3 in June, 78.1 in July, 76.0 in August and 60.3 in September. Five monthly declines in a row have not happened since the run that ended in April 2016, during the declining phase of Solar Cycle 24, and before that in early 2003.
Averages point the same way
Single months can swing widely, so averages give a steadier picture. From August to October 2026 the sunspot number averaged 60.7, the lowest three-month average since the three months to January 2022. Over the 12 months to October it averaged 85.8, down from 131.2 over the previous 12 months and the lowest 12-month average since the year to December 2022.
From January to October 2026 the monthly figure averaged 81.3, compared with 126.6 in the same months of 2025 and 154.6 in 2024. SILSO's yearly mean was 154.7 in 2024, the highest since 2002, and 123.2 in 2025.
Where Solar Cycle 25 stands
Solar Cycle 25 began at the minimum of December 2019. Monthly activity peaked in August 2024 at 216.0, the highest monthly sunspot number since September 2001. The 13-month smoothed sunspot number, the measure used to date a cycle's maximum, reached 160.9 in October 2024. Because the smoothing needs six months of data on either side, the latest smoothed value is for April 2026: 88.6, the lowest since July 2022 (86.7).
Solar cycles last about 11 years on average, so a decline roughly two years after the maximum is expected. A low October does not mean the minimum is close: in the last cycle, the monthly number had fallen to 33.4 by October 2016, two and a half years after that cycle's smoothed maximum, yet the minimum did not arrive until December 2019. Large flares and geomagnetic storms can still occur during the declining phase, but lower activity generally means less heating of the upper atmosphere and less drag on satellites in low Earth orbit.
About the data
Monthly values are the international sunspot number (version 2.0) from WDC-SILSO, Royal Observatory of Belgium, Brussels, published under the CC BY-NC 4.0 licence. The October 2026 value comes from SILSO's monthly file; earlier months in the PolarisWire tracker also appear in NOAA Space Weather Prediction Center's observed solar cycle indices, and all 225 monthly values from January 2008 to September 2026 match the SILSO file. Smoothed values and yearly means come directly from SILSO. The October mean of the 10.7 cm radio flux will be added to the tracker once NOAA SWPC publishes it.
The full monthly series since 2008 is available in the PolarisWire Solar Cycle 25 tracker, which is updated daily and offers a CSV download, while the solar cycle statistics page and the sunspot cycle lookup cover the record back to 1749. The figures and charts can be reused for non-commercial purposes under CC BY-NC 4.0 with credit to PolarisWire and WDC-SILSO.
What was the sunspot number in October 2026?
The monthly mean international sunspot number was 45.7 in October 2026 (provisional, WDC-SILSO), the lowest since November 2021 and the fifth monthly decline in a row. Solar Cycle 25 peaked with a monthly value of 216.0 in August 2024 and a smoothed maximum of 160.9 in October 2024.
Sources & further reading
- Monthly mean total sunspot number, WDC-SILSO, Royal Observatory of Belgium, Brussels ↗sidc.be
- Solar Cycle Progression (NOAA Space Weather Prediction Center) ↗swpc.noaa.gov
- PolarisWire Solar Cycle 25 tracker: monthly sunspot numbers and F10.7 flux ↗polariswire.com
- PolarisWire solar cycle statistics: key figures since 2008 ↗polariswire.com
- Sunspot number and F10.7 flux by month since 2008, spreadsheet file ↗polariswire.com
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