A partially concealed sunspot behind the southeastern limb of the Sun unleashed a powerful M 9.6 solar flare directed towards Earth. Although the sunspot was not facing our planet, the effects of the eruption were felt. The resulting radiation triggered a moderate radio blackout in parts of North America, Central America, and South America, according to the Space Weather Prediction Center of NOAA (ref.).
Classification of solar flares
Due to the rotation of the Sun, the hidden sunspot will become visible from Earth over the weekend, directly in front of us. Solar flares occur when magnetic energy accumulates in the solar atmosphere and is released in an intense explosion of electromagnetic radiation.
These events are classified by size into letter groups, with class X being the most powerful. Class M flares are 10 times weaker than class X flares. Following class M are class C, class B, and finally class A flares, which are too weak to significantly affect life on Earth.
Within each class, numbers from 1 to 10 denote the relative strength of the event. The recent solar flare reached M 9.6. If it had been 4% brighter, it would have been classified as class X. According to SpaceWeather.com, it is likely that it was indeed a partially eclipsed class X flare at the edge of the Sun, and therefore recorded only as class M.
Consequences of the flare
Although it was obscured behind the solar disk, the M-class solar flare still caused extensive radio blackouts due to the strong X-ray and extreme ultraviolet radiation pulses sent towards Earth. Traveling at the speed of light, the radiation reached our planet in eight minutes.
The radiation ionized the thermosphere, triggering shortwave radio blackouts in the sunlit part of the Earth at that time. Solar activity is increasing as part of Solar Cycle 25, which scientists predict will peak in 2025.