Solar Cycle
The Sun follows an approximately 11-year activity cycle driven by the reversal of its magnetic field. During each cycle, the number of sunspots rises from a quiet minimum to an active maximum and back again. We are currently in Solar Cycle 25, which began in December 2019 and is approaching or just past its solar maximum.
Solar Cycle 25 Progress
Predicted smoothed sunspot number (blue line) with the forecast uncertainty range (shaded band) compared to actual monthly observations (orange dots). The prediction is issued by the NOAA/NASA Solar Cycle 25 Prediction Panel.
Where Are We Now?
Solar maximum for Cycle 25 was originally forecast around July 2025, with a relatively modest peak sunspot number of roughly 115. However, observed activity has consistently exceeded predictions since mid-2023, and many solar physicists now consider Cycle 25 to be significantly stronger than initially expected, with observed monthly sunspot numbers surpassing 180 at times.
The peak of solar maximum appears to have occurred in late 2024 into early 2025, though elevated activity can persist for months on either side of the statistical peak. Even as the cycle eventually declines, periods of intense solar activity remain possible for several years.
10.7 cm Solar Radio Flux (Last 30 Days)
The F10.7 index measures solar radio emission at a wavelength of 10.7 cm (2800 MHz). It is one of the longest-running records of solar activity and serves as an excellent proxy for overall solar output. Values below 70 SFU indicate quiet conditions, while values above 150 SFU correspond to elevated activity. During solar maximum, daily values frequently exceed 200 SFU.
What Does Solar Maximum Mean for Space Weather?
Solar maximum is the most active phase of the solar cycle. During this period the Sun produces significantly more sunspots, solar flares, and coronal mass ejections (CMEs). These events drive the most impactful space weather:
- More frequent and powerful solar flares — X-class flares become more common, producing intense bursts of radiation that can disrupt HF radio communications and GPS accuracy within minutes.
- Increased coronal mass ejections — Large CMEs can trigger geomagnetic storms when they reach Earth, potentially affecting power grids, satellite operations, and spacecraft electronics.
- Aurora visible at lower latitudes — Strong geomagnetic storms push the auroral oval toward the equator, making the Northern and Southern Lights visible far from the poles. During Cycle 25, aurora have been observed as far south as the mid-latitudes of the United States and Europe on multiple occasions.
- Elevated radiation environment — Solar energetic particle events increase, posing risks to astronauts, high-altitude aviation, and sensitive satellite components.