Earth hit by biggest 'solar radiation storm' in 23 years, triggering Northern Lights as far as Southern California

Update, Wednesday (Jan. 21) at 11 a.m. ET: Geomagnetic conditions are starting to settle, but auroras are still highly likely in the northern tier of the United States tonight, according to NOAA's latest forecasts. Strong (G3-level) geomagnetic storms remain possible overnight, so be sure to check the skies after dark.

A "severe" and record-breaking geomagnetic storm rocked Earth's magnetic shield last night, shortly after the sun unleashed a powerful X-class solar flare. The epic event, triggered by a stream of superfast solar particles, painted widespread auroras at unusually low latitudes across the Northern Hemisphere, particularly in Europe.

Some outlets have reported that the storm is the "largest" of its kind since 2003, which is an exaggeration (the "Mother's Day storm" of May 2024 was much stronger). However, the latest outburst has broken a specific 23-year-old solar radiation record.

The geomagnetic storm began on Monday (Jan. 19), when a fast-moving cloud of solar radiation, or coronal mass ejection (CME), slammed into Earth's magnetosphere, temporarily disrupting the invisible magnetic field lines surrounding our planet and allowing charged particles to penetrate deeper into the atmosphere. The CME was initially released on Sunday (Jan. 18) when an X1.9 magnitude solar flare suddenly exploded from a dark patch near the sun's equator, Live Science's sister site Space.com reported.

Geomagnetic activity first peaked at 2:38 p.m. EST, when the storm reached G4 ("severe") status, according to the National Oceanic and Atmospheric Administration's (NOAA) Space Weather Prediction Center (SWPC). The storm calmed slightly before reaching G4 status again at 3:23 a.m. EST on Tuesday (Jan. 20), according to a second SWPC report.

G4 is the second-highest level a geomagnetic storm can reach. Under these conditions, solar radiation can cause temporary radio blackouts, disrupt or damage orbiting spacecraft and impact some ground-based infrastructure. However, it is too early to tell what specific issues this storm caused, if any.

There were widespread aurora displays across the U.K. and parts of Europe — including France, Germany, Switzerland, Austria, Belgium, Norway, Denmark, the Netherlands and Croatia — where the sun had already set before the storm peaked, according to Spaceweather.com.

Experts had predicted that up to 24 U.S. states would see auroras during the storm, according to Space.com. It is unclear if this actually happened, especially as the storm's first peak occurred before sunset in North America. However, skywatchers as far south as Alabama, Georgia, New Mexico and California reported seeing auroras overnight, according to Spaceweather.com.

More auroras are possible tonight, according to Space.com's latest aurora forecast. However, the storm is not expected to reintensify to G4 status.

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A 23-year record

Despite some initial reports, last night's display was not the biggest geomagnetic storm of the past two decades. That title goes to the "Mother's Day storm" of May 2024, which reached G5 ("extreme") status for the first time since the infamous "Halloween solar storms" of 2003.

The 2024 storm was triggered by at least five successive CMEs that exploded from an unusually active sunspot, saturating the upper atmosphere with radiation for three days. This caused some of the most widespread auroras in centuries and temporarily transformed the "radiation belts" surrounding our planet.

However, while the latest storm did not reach the heights of 2024's disturbance, it was one of the most powerful "solar radiation storms" on record.

The term solar radiation storm refers to a solar outburst, like a CME, as it travels through space, rather than the actual effect it has on our planet. Big radiation storms often lead to powerful geomagnetic storms, but other factors influence how Earth's magnetic field will respond, such as the orientation of the incoming radiation and its magnetic configuration.

The solar radiation storm that sparked last night's auroras reached S4 ("severe") status — the equivalent of G4 on the solar radiation storm scale. This is the first time this has happened since 2003's Halloween storms, SWPC representatives wrote on the social platform X.