Discover more about the Sun’s solar cycle and how it impacts us here on Earth – from increased auroras to failing power grids
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The solar cycle is a natural rhythm that controls the activity of the Sun and influences the frequency of solar phenomena such as sunspots, solar flares, and coronal mass ejections. However, the solar cycle affects more than just the Sun.
During periods of high activity, solar storms can affect us here on Earth too. Read on to find out what the solar cycle is, how it works, and the surprising ways that it can impact our planet.
The solar cycle
The solar cycle describes an approximately 11-year cycle of solar activity driven by the sun’s magnetic field and indicated by the frequency and intensity of sunspots visible on the star’s surface. While solar cycles are repetitive, they can be difficult to predict, with some cycles lasting only eight years while others continue for 14.
Each cycle has phases known as solar minimum and solar maximum. During the solar minimum, sunspot activity is low, and solar storms are rare. As the cycle progresses toward solar maximum, sunspot numbers increase, along with the frequency of solar flares and solar storms.
Solar storms occur when the Sun releases bursts of charged particles and magnetic energy, which can travel toward Earth. These storms are often triggered by solar flares and coronal mass ejections (CMEs), especially during the active phases of the solar cycle.
Our Earth is currently in solar cycle 25, which began in December 2019, according to NASA. Solar activity has increased since then, with 2024 looking to have been the solar maximum of the cycle.
The cause of the solar cycle
Every 11 years or so, the sun’s magnetic field flips, making the north become south and the south become north. Changes to the magnetic field affect the activity on the sun’s surface.
When this flipping of the poles occurs, the effects ripple throughout the solar system, extending for billions of miles, beyond any of our planets. Planets without a magnetosphere feel much more dramatic impacts than Earth. For example, when the sun ejected plasma in 2006, Venus was stripped of a vast amount of oxygen due to its lack of protection.
The flipping of magnetic poles is not unique to the Sun however. Earth also experiences a reversal of its magnetic field, although its cycle is much longer, averaging around 300,000 years. The next pole reversal is long overdue as scientists believe it has now been 780,000 years since the last.
How does the solar cycle affect us?
The effects of the solar cycle here on Earth are thought to be very minor in comparison to other planets due to our protective atmosphere and magnetosphere. While the activity can affect astronauts and equipment in space, the biggest concern on Earth is the effects of increased radiation on high-frequency equipment, power grids and GPS.
Huge solar flares could lead to a radio blackout on Earth if the electromagnetic energy becomes too disruptive. This disruption occurs mainly in the ionosphere, where long-distance communications signals travel, and can lead to radio blackouts globally.
During solar storms, fast-moving charged particles are emitted, and carry huge amounts of energy that can damage astronauts and spacecraft. When storms are predicted or detected, astronauts on the International Space Station must seek shelter from the radiation and are not permitted to carry out experiments or activities outside of the spacecraft. To prevent damage to satellites and space equipment, radiation-sensitive systems are powered off until the storm has passed too.
A couple of days after a solar eruption heads towards Earth, CMEs can hit the planet’s magnetosphere and induce currents in electrical systems. This makes power grids vulnerable to surges and can cause blackouts.
So what exactly are some events that have happened on Earth as a direct result of solar cycles?
The 1972 Vietnam solar storm
The August 1972 solar storm marked one of the first instances where a solar event significantly disrupted modern technology, impacting both satellite communications and military operations during the Vietnam War. The disruption was caused by a powerful solar flare that erupted from the Sun, followed by a CME that reached Earth in just 14.6 hours – an unusually fast time for an ejection to travel, proving how powerful the solar flare must have been.
Satellites experienced huge unexpected outages and signal interference, hindering naval operations off the coast of Vietnam, as communications between ships and commands were severely impacted.
Even more concerningly, the storm set off hundreds of underwater mines near Haiphong, North Vietnam. It is suggested that the mines were likely triggered by magnetised gas that reached the Earth after being ejected by the Sun. The mines had been previously placed by the US Navy, and their unexplained detonations raised concerns about the stability of other military equipment in extreme solar conditions.
The 1972 event highlighted the growing vulnerability of satellites, communication systems, and electrical infrastructure to solar activity, marking a turning point in recognising the need to study and prepare for solar storms.
The 1989 Quebec blackout
On March 13th 1989, a powerful CME hit Earth’s magnetic field and within 90 seconds, the Hydro-Quebec power grid began to fail.
This burst of solar particles from the CME interacted with Earth’s magnetic field, creating powerful geomagnetic currents that surged through the ground in Quebec. These currents overloaded the electrical grid, causing protective relays to trip and resulting in a province-wide blackout lasting for about nine hours.
The outage affected millions, halting essential services and daily operations. To resolve it, Hydro-Québec reinforced the grid’s resilience, upgrading its grounding systems and adding protective devices to limit future disturbances from geomagnetic storms.
The incident was one of the first to prove the vulnerability of power grids to space weather, prompting global utilities to adopt protective measures against similar solar storm disruptions.
The Carrington Event
The Carrington Event was the largest solar storm in recorded history, occurring at the beginning of September 1859, a few months before the solar maximum in 1860.
It began on 1 September when British astronomer Richard Carrington saw an intense solar flare – a sudden burst of energy on the Sun’s surface while observing and sketching the changing sunspots.
The next day, a massive CME reached Earth, triggering extreme geomagnetic storms, leading Carrington to deduce that what he witnessed on the Sun’s surface was affecting the Earth, dubbing it the ‘Carrington Event’.
The Carrington Event caused auroras that were visible as far south as the Caribbean and disrupted telegraph systems worldwide. The storm also had effects on telegraph lines, causing sparks to fly from the masts and even igniting fires. Some operators reported electric shocks and were even able to still send messages when the power was disconnected due to the huge surge of energy through the lines.
Increased auroras
One spectacular side effect of increased solar activity during the solar cycle is the increased opportunities to see the aurora borealis and the aurora australis. You might have caught a glimpse of them during one of their several shows in the night sky over the UK this year!
The auroras occur due to the energetic particles from the Sun colliding and interacting with the Earth’s upper atmosphere, creating dazzling light displays across the sky. The colour of the aurora depends on what chemicals in the atmosphere the particles hit.
Red tones are produced from collisions with nitrogen molecules, while oxygen molecules are responsible for green hues.
Solar activity and Earth’s climate
The IPCC has found that changes in solar activity only play a very minor role in Earth’s climate, with greenhouse gases playing a much larger role in the warming of the planet.
Satellites in space have observed the sun’s energy output for over 40 years and determined that the value has only fluctuated by less than 0.1 per cent during that period. Since 1750, the warming driven by greenhouse gases coming from the human burning of fossil fuels is over 270 times greater than the slight extra warming coming from the Sun itself over that same time interval.
