A solar flare is a sudden, intense burst of electromagnetic radiation from the Sun's surface, typically near sunspots. Flares are classified by their X-ray intensity using the A, B, C, M, X scale — each class is ten times stronger than the previous. M-class and X-class flares can cause radio blackouts and radiation storms on Earth.
Solar flares occur when magnetic energy built up in the solar atmosphere is suddenly released, heating plasma to millions of degrees and accelerating charged particles. They typically last minutes to hours.
**Flare classification (GOES X-ray flux):**
- **A-class:** Background level, no impact
- **B-class:** Very small, no consequences
- **C-class:** Small, minor HF radio impact on sunlit side
- **M-class:** Medium, can cause brief radio blackouts and minor radiation storms
- **X-class:** Major, can cause planet-wide radio blackouts and long-lasting radiation storms
Each class is further divided 1–9 (e.g. M5 is half of X1). X-class flares are the most powerful and can trigger coronal mass ejections (CMEs) that reach Earth 1–3 days later.
Flarient displays live GOES X-ray flux data from NOAA on the homepage and Solar Flares page.
Evidence & Sources
Solar flares release magnetic energy as electromagnetic radiation
Flares are classified A, B, C, M, X by X-ray flux
X-class flares can cause planet-wide radio blackouts
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Last reviewed: 21 August 2026