Solar Superstorms: Flares, CMEs and How Space Weather Affects Earth

The Sun looks calm and steady from Earth, but it is a churning ball of hot, electrically charged gas called plasma, threaded with tangled magnetic fields. Every so often those fields snap and release enormous amounts of energy. The documentary above, Solar Superstorms (first broadcast in 2012), takes viewers inside that activity. This guide explains the key ideas, and brings the story up to date with the powerful storms of the current solar cycle.

The Sun’s 11-year cycle

Solar activity rises and falls over a cycle of roughly 11 years. At solar minimum the Sun may show few or no sunspots for weeks. At solar maximum there can be dozens, along with frequent eruptions. Sunspots are darker, cooler regions where strong magnetic fields poke through the surface and block some of the heat flowing up from below. The current cycle, Solar Cycle 25, began in December 2019, and NASA and NOAA announced in October 2024 that the Sun had reached its maximum period.

Solar flares

A solar flare is a sudden, intense burst of radiation from a magnetically active region, usually near sunspots. Flares release energy across the spectrum, from radio waves to X-rays, and the light reaches Earth in about eight minutes. Flares are ranked by X-ray strength in classes A, B, C, M and X, with each class ten times stronger than the one before. Strong flares can disrupt high-frequency radio communication on the sunlit side of Earth.

Coronal mass ejections

A coronal mass ejection, or CME, is a huge cloud of plasma and magnetic field thrown off from the Sun’s outer atmosphere, the corona. A large CME can carry billions of tonnes of material and typically takes one to three days to reach Earth. CMEs often accompany flares, but not always. When a CME’s magnetic field is oriented opposite to Earth’s, it can couple strongly with our planet’s magnetic field and trigger a geomagnetic storm.

Auroras and geomagnetic storms

Earth’s magnetic field and atmosphere protect us at ground level from the harmful radiation in these events. But when a CME hits, energy is funnelled into the upper atmosphere near the poles, where charged particles collide with oxygen and nitrogen and make them glow. That glow is the aurora: the northern lights (aurora borealis) and southern lights (aurora australis). During strong storms, auroras can be seen much closer to the equator than usual.

NOAA’s Space Weather Prediction Center rates geomagnetic storms on a scale from G1 (minor) to G5 (extreme). Strong storms can induce currents in long power lines and pipelines, disturb GPS signals, and increase drag on satellites in low orbit.

History’s great solar storms

1859: The Carrington Event. British astronomer Richard Carrington saw a brilliant white-light flare on 1 September 1859. Within about a day, auroras were seen as far south as the Caribbean, and telegraph systems sparked and failed. It remains the most intense geomagnetic storm on record.

March 1989: Quebec blackout. A powerful storm caused the Hydro-Quebec power grid in Canada to collapse in about 90 seconds, leaving millions of people without power for around nine hours.

October 2003: The Halloween storms. A series of very large flares and CMEs disrupted satellites and forced airlines to reroute some polar flights.

May 2024: The Gannon storm. On 10-11 May 2024, a cluster of CMEs produced the first G5 (extreme) geomagnetic storm since 2003. Auroras were photographed across much of the United States, Europe and even at lower latitudes. Grid operators took precautions and there were no major blackouts, although some satellites and GPS-guided farm equipment were affected. NOAA notes that it was still considerably weaker than the 1859 Carrington event.

How scientists keep watch

A fleet of spacecraft monitors the Sun around the clock. NASA and ESA’s SOHO observatory, NASA’s Solar Dynamics Observatory, and spacecraft stationed about 1.5 million km sunward of Earth give forecasters advance warning. NASA’s Parker Solar Probe has flown closer to the Sun than any human-made object, passing through the corona itself, while ESA’s Solar Orbiter is studying the Sun’s poles. Forecasters at NOAA and other agencies use these data to issue space weather watches and warnings, much like weather forecasters on the ground.

Can you observe solar activity yourself?

Yes, but only with proper protection. Never look at the Sun directly, or through binoculars or a telescope without a certified solar filter that covers the front of the instrument. With a safe white-light filter you can watch sunspots change from day to day. Dedicated hydrogen-alpha solar telescopes show prominences and flares on the Sun’s edge. And when a strong storm is forecast, simply stepping outside after dark, away from city lights, may reward you with an aurora. Phone cameras often pick up aurora colours that are too faint for the eye.