Sunspots fall to their lowest level since January 2022 as Solar Cycle 25 winds down
The monthly sunspot number dropped to 60.3 in September 2026 and solar radio flux to 105.4 sfu, both the lowest since January 2022, down about 72% and 57% from the August 2024 peak.
The story in focus
The Sun's monthly sunspot number fell to 60.3 in September 2026, the lowest reading since January 2022, according to the PolarisWire Solar Cycle 25 tracker built on NOAA Space Weather Prediction Center and WDC-SILSO data. Solar radio flux at 10.7 cm dropped to 105.4 solar flux units, also its lowest since January 2022. Both measures are now well below the peak of August 2024, a sign that Solar Cycle 25 is past its maximum and heading toward its next minimum.
- The monthly mean sunspot number was 60.3 in September 2026 (provisional), down from 76.0 in August and 129.7 in September 2025, and the lowest since 55.3 in January 2022.
- F10.7 solar radio flux averaged 105.4 sfu in September 2026, down 31.5% from 153.9 a year earlier and the lowest since January 2022 (104.0).
- The cycle's highest month was August 2024, with a sunspot number of 216.0 and flux of 245.6 sfu; September 2026 is 72% and 57% below those levels.
- The 13-month smoothed sunspot number peaked at 160.9 in October 2024, well above Solar Cycle 24's 116.4 maximum, and has since fallen to 94.4 (March 2026).
What the latest data show
The international sunspot number, compiled by the World Data Center SILSO at the Royal Observatory of Belgium and published by NOAA's Space Weather Prediction Center, averaged 60.3 in September 2026. That is down from 78.1 in July and 76.0 in August, and less than half the 129.7 recorded in September 2025. No month has had a lower value since January 2022, when the figure was 55.3. SILSO lists all 2026 monthly values as provisional, so they can still be revised slightly.
The 10.7 cm solar radio flux, an independent measure of solar activity recorded by Natural Resources Canada, tells the same story. It averaged 105.4 solar flux units (sfu) in September 2026, compared with 116.2 in August and 153.9 a year earlier. That was also the lowest monthly value since January 2022 (104.0 sfu).
A steady slide from the 2024 peak
Solar Cycle 25 began at the minimum of December 2019, when the 13-month smoothed sunspot number was 1.8. Monthly activity peaked in August 2024 at 216.0, the highest monthly sunspot number since September 2001, with radio flux reaching 245.6 sfu in the same month. The smoothed sunspot number, the measure used to date a cycle's maximum, reached 160.9 in October 2024. That was well above the 116.4 peak of Solar Cycle 24 in April 2014, though below Solar Cycle 23's 180.3 in November 2001.
Since then, activity has declined. The yearly mean sunspot number was 154.7 in 2024, the highest since 2002 (163.6), and 123.2 in 2025. From January to September 2026 the monthly sunspot number averaged 85.3, against 127.9 in the same months of 2025 and 153.3 in 2024. The average for July to September 2026 was 71.5, the lowest three-month average since the three months to March 2022. The latest smoothed value available, for March 2026, is 94.4, the lowest since August 2022 (92.6).
What it means
Solar cycles last about 11 years on average, so a decline about two years after the maximum is expected. Monthly values jump around a lot, so a single low month does not mean the cycle has reached its minimum. Over the 12 months to September 2026, the sunspot number averaged 91.5, compared with 135.4 over the previous 12 months, and radio flux averaged 133.4 sfu against 169.5 sfu.
Lower activity generally means fewer strong solar flares and radio blackouts. It also means less heating of the upper atmosphere, which reduces drag on satellites in low Earth orbit. Space weather forecasters note that large flares and geomagnetic storms can still happen during the declining phase of a cycle, so a quieter Sun is not a risk-free Sun.
About the data
Monthly sunspot numbers are the international sunspot number (version 2.0) from WDC-SILSO, Royal Observatory of Belgium, as distributed in NOAA SWPC's observed solar cycle indices. F10.7 values are monthly means of the 10.7 cm radio flux measured in Penticton, Canada. Smoothed values and yearly means come directly from SILSO. Every monthly value in the PolarisWire tracker since January 2008 was checked against both the NOAA SWPC and SILSO files and matched.
The full monthly series since 2008 is available in the PolarisWire Solar Cycle 25 tracker, which is updated daily and offers a CSV download and an embeddable chart.
What is the current sunspot number?
The monthly mean international sunspot number was 60.3 in September 2026 (provisional), the lowest since January 2022 and down from 129.7 in September 2025. 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
- Solar Cycle Progression (NOAA Space Weather Prediction Center) ↗swpc.noaa.gov
- Sunspot number series, WDC-SILSO, Royal Observatory of Belgium ↗sidc.be
- PolarisWire Solar Cycle 25 tracker: monthly sunspot numbers and F10.7 flux ↗polariswire.com
- Sunspot number and F10.7 flux by month since 2008, spreadsheet file ↗polariswire.com
Help keep the record accurate. Send a correction.
