Are we in the largest solar radiation storm in 20 years?

You probably can’t tell, but we are currently experiencing one of the strongest storms to hit the Earth in more than two decades. It’s not a meteorological event though — it’s the biggest solar radiation storm since 2003.

The Space Weather Prediction Center (SWPC) of the National Oceanic and Atmospheric Administration has been monitoring the storm, which reached Earth on Monday and is expected to last a few days. It’s caused by charged particles from the sun and has been ranked a 4 out of 5 in severity. This is different from a geomagnetic storm, which is caused by a coronal mass ejection of plasma from the sun and is known for causing auroras in Earth’s atmosphere.

Solar radiation storms this strong are rare and cause increased radiation exposure risks for astronauts and electrical equipment. When the last S4 storm hit in October 2003, it caused damage to power systems in Sweden and South Africa that in some cases resulted in power outages. The SWPC is keeping NASA and other agencies informed of potential concerns related to the storm, which is expected to weaken over the next few days.