Earth was just hit by the strongest solar radiation storm in over 20 years — here's what it means

A portion of the solar radiation storm captured on Jan. 19. The incoming protons look like a 'snowstorm' on the SOHO spacecraft's LASCO instrument. The bright specks of light in the frame are Venus, Mercury and Mars. (Image credit: ESA/SOHO)

While a severe G4 geomagnetic storm impressed skywatchers with vivid auroras around the world this week, a far less visible, but historically significant, space weather event was also underway.

On Monday (Jan. 19), Earth experienced its strongest solar radiation storm since October 2003, according to NOAA's Space Weather Prediction Center, surpassing the intensity of the notorious October 2003 "Halloween" space weather storms.