A solar flare is a sudden, intense burst of radiation from the Sun’s surface, released when tangled magnetic fields near sunspots snap and reconnect. A large flare can release as much energy as billions of nuclear bombs in a few minutes.
Flare classes
Flares are ranked by their peak X-ray brightness, measured by satellites. Each letter is ten times stronger than the previous one:
A and B: the weakest, close to background levels.
C: small, with few noticeable effects on Earth.
M: medium, can cause brief radio blackouts near the poles.
X: the strongest. An X2 flare is twice as strong as X1, and the scale continues above X10.
The record holder in the satellite era is a flare in November 2003, so strong it saturated the detectors; it was estimated around X28 or higher.
Credit : whatcanu.com
Flares vs coronal mass ejections
Flares are often confused with coronal mass ejections (CMEs):
A flare is a flash of light and radiation, reaching Earth in about 8 minutes.
A CME is a huge cloud of magnetized plasma hurled into space. It takes one to several days to reach Earth.
They often occur together, but not always. CMEs cause most geomagnetic storms and the brightest auroras.
Effects on Earth and in space
Radio blackouts: X-rays ionize the upper atmosphere on the sunlit side of Earth and disrupt high-frequency radio used by aviation and ships.
Navigation: GPS accuracy can decrease.
Solar radiation storms: energetic particles can endanger astronauts and affect polar flights and satellites, see cosmic rays.
Geomagnetic storms (from CMEs): can disturb power grids and satellites and push auroras toward lower latitudes. The Carrington Event of 1859 set telegraph lines on fire. In May 2024, a strong storm produced auroras visible far from the poles.
Flares do not harm people on the ground: the atmosphere absorbs their radiation.
Credit : whatcanu.com
The solar cycle
Solar activity rises and falls over about 11 years. In October 2024, NASA and NOAA announced that the Sun had reached the maximum period of Solar Cycle 25, so large flares remain more frequent than at solar minimum for a while. See the role of the Sun in the solar system.
Where to follow space weather
The NOAA Space Weather Prediction Center publishes forecasts, alerts and scales for radio blackouts (R1 to R5), radiation storms (S1 to S5) and geomagnetic storms (G1 to G5). Aurora forecasts are useful if you hope to see the northern lights.
