On September 6, 2017, the sun emitted a powerful X-class solar flare — a designation reserved for the most intense flares. Seen here in ultraviolet light captured by NASA’s orbiting Solar Dynamics Observatory, the flare was one of the strongest seen in years and came amid a spate of solar eruptions that month. The glowing threads are scorching filaments of plasma ensnared by magnetic fields arcing over the Sun’s surface.