Fact-Checking Solar Cycle 25: Is the Sun Actually Getting Brighter Every Year?
The primary argument raised by internet theorists claims that the current 11-year sunspot sequence, Solar Cycle 25, has elevated solar brightness to historically dangerous highs. Heliophysicists track this metric using space-based radiometers to calculate Total solar irradiance (TSI), the amount of solar power reaching the top of Earth's atmosphere per square meter.
Precision satellite platforms, including NASA's SORCE and the TSIS-1 instrument mounted on the International Space Station, reveal that TSI fluctuates along with the 11-year magnetic cycle. During solar maximum, when sunspots and bright magnetic features called faculae pepper the photosphere, total output increases. But the scale of that change surprises most non-scientists.
| Solar Cycle Period | Peak Activity Window | Smoothed Sunspot Number (Peak) | Total Solar Irradiance Variance (TSI) |
|---|---|---|---|
| Cycle 22 (1986, 1996) | 1989, 1991 | 212.5 | ~1.3 W/m² (~0.10%) |
| Cycle 23 (1996, 2008) | 2000, 2002 | 180.3 | ~1.2 W/m² (~0.09%) |
| Cycle 24 (2008, 2019) | 2012, 2014 | 116.4 | ~0.9 W/m² (~0.07%) |
| Cycle 25 (2019, 2030) | 2024, 2026 | ~160, 175 (Observed) | ~1.1, 1.3 W/m² (~0.09%) |
The solar constant hovers at roughly 1,361 Watts per square meter. Across the entire 11-year cycle, total solar irradiance swings by approximately 0.1%. That is a shift of barely one watt over a field of intense output. While Cycle 25 has outperformed early consensus forecasts that anticipated a quiet cycle like Cycle 24, its peak outputs remain well within normal limits established across centuries of observation.
