The people of Earth have been observing the effects of space weather for millennia, long before we sent our vessels skywards.
Mesopotamian stone tablets dating back over 2,500 years describe red clouds and glowing skies, now thought to be the first written account of the aurora borealis or Northern Lights.
These eerie lights were feared by early observers, who described them as bad omens or roaming dragons lighting up the night with their fiery breath.
The chemistry behind aurora
We now know that the ‘flames’ are not caused by vengeful dragons but by charged particles, mostly protons and electrons, interacting with Earth’s magnetic field and atmosphere.
Known as the solar wind, these charged particles are constantly flowing from the Sun out into space at over a million miles an hour, bombarding our planet and everything else in the Solar System with radiation.
Fortunately, our magnetosphere, the shield created by Earth’s magnetic field, does a good job of protecting us from this onslaught.
When the intensity of the radiation is high enough, the particles can funnel along our magnetic field lines at the poles and down into our atmosphere, energising the gases there to create the beautiful dancing displays of light we know as the aurora.
Ejections and flares
In addition to providing the ever-present solar wind, the Sun can suddenly belch huge amounts of radiation out into space in the form of solar flares or coronal mass ejections (CMEs).
Solar flares are sudden bright flashes of electromagnetic energy travelling at the speed of light, while CMEs are part of the solar atmosphere thrown out in enormous clouds of plasma.
Although quite different, they often occur together and can be collectively described as solar storms.
The frequency of these storms depends on where we are in the Sun’s somewhat predictable 11-year cycle of activity, known as the solar cycle.
At solar maximum, the Sun is at its most violent and active, with huge eruptions more commonplace, while at solar minimum it settles down like a sleeping giant – quiet for a time but certain to wake with a temper.
If directed towards Earth, a CME can cause disruption to our magnetosphere, known as a geomagnetic storm. These can last for many hours.
During such times, we ground dwellers are treated to more powerful aurorae, often extending down to lower latitudes.
In addition to the aurora, the influx of charged particles can cause a whole host of problems for our technological society.
The changing magnetic field can cause unexpected currents to flow in electrical cables, causing power cuts, electrical disturbances and damage to underground pipelines.
Stories dating back hundreds of years talk of ships running aground due to mysterious compass bearing errors, evoking images of sailors stranded on the rocks, staring up in wonderment, as the aurora danced above.
In 1859, an enormous solar flare and associated CME, known as the Carrington Event, produced aurorae said to be the most breathtaking ever seen.
Meanwhile, the currents it induced at ground level ran amok, disabling telegraph systems around the world.
Telegraph operators reported electric shocks, sparks flying and being able to send messages even after the system was disconnected, as if it was working by magic.
The storms also change the density of Earth’s upper atmosphere, the ionosphere, leading in modern times to radio blackouts, GPS positioning errors and increased atmospheric drag on satellites.
Space weather and the danger to spacecraft
Without the full protection of our atmosphere and magnetic field, spacecraft are particularly vulnerable to the effects of space weather.
Charged particles can cause currents to flow in unexpected places, leading to electrical discharge that can damage sensitive components.
Random signals cause systems to turn on and off, or thrusters to suddenly fire, as if there is a ghost in the machine.
Any spacecraft using solar cells can expect a gradual drop in efficiency as the solar wind blasts their surfaces, causing an increase in electrical resistance, but a severe storm can multiply this effect many times over.
These effects can be mitigated somewhat by careful design and shielding, but weight is money when it comes to spaceflight and there is a trade-off between a failsafe design and the cost of the mission.
Whenever there is an electrical fault, spacecraft are programmed to go into safe mode, ceasing any operations that are not strictly necessary and pointing their solar panels at the Sun to maintain power.
This gives the ground crew time to work the problem.
Space weather forecasting by organisations such as the USA’s National Oceanic and Atmospheric Administration (NOAA) can sometimes give notice that a storm is imminent, allowing spacecraft to be switched into safe mode in advance, protecting sensitive systems.
Space weather effect on humans
The 2003 storms sent ISS astronauts Michael Foale and Alexander Kaleri running – or floating – for cover.
They sheltered in the Zvezda service module, the most shielded location aboard the ISS, cutting their radiation exposure by 50%.
The ISS orbits within Earth’s magnetosphere and this, along with the shielding provided by the station, is enough to keep astronauts safe when the weather outside is lousy.
For explorers heading further afield, such as the Artemis astronauts returning to the Moon, or future Mars colonists, it’s a different story.
In August 1972, between Apollo 16 and 17, there were a series of powerful solar storms that would have given the astronauts radiation sickness had they been in space at the time.
The situation wouldn’t have been much better had they been at their destination, since the Moon doesn’t have much in the way of a magnetic field or atmosphere.
In fact, if astronauts had been walking on the Moon in August 1972 without the protection of their spacecraft, the result could have been fatal.
Careful spacecraft design and improved space weather forecasting will both be essential to protect future long-distance voyagers, and it may be wise for them to construct subterranean colonies when they arrive, utilising layers of rock and soil for protection from radiation.
Space weather and solar maximum
Solar maximum occurs because the Sun is made of plasma, an intensely hot soup of charged particles that, when in motion, generate magnetic fields.
At solar minimum, the magnetic field of the Sun has a relatively simple shape that is concentrated at the poles.
However, the Sun rotates faster at the equator than at the poles, and this rotating plasma drags the magnetic field around with it, causing it to become more and more tangled and complex.
This violent twisting of the magnetic field drives the formation of sunspots, flares and coronal mass ejections.
When we reach solar maximum, the magnetic field is in its most chaotic state and the number of sunspots and violent eruptions peaks.
At this point, the Sun’s magnetic field flips, the north pole becomes the south and vice versa, and the Sun begins to settle again as we journey towards the next minimum.
This article appeared in the June 2025 issue of BBC Sky at Night Magazine
