Geomagnetic storms are capable of sparking beautiful displays of the Northern Lights across our night sky. However, there is a potential danger behind that beauty, especially now, with solar activity running at maximum. Here's a guide to when we should look up, and when we should worry.

In our sky, the Sun appears steady and unchanging. However, hidden by the bright glare, there is a lot going on right now. Dark sunspots mar its bright surface, solar flares blast out x-rays and uv radiation, immense coronal mass ejections erupt into space, and coronal holes emit energetic streams of solar particles that interrupt the normally sedate flow of the solar wind.

In this artist's representation, magnetized solar matter forms loops between dark sunspots, while a solar flare causes the eruption of a coronal mass ejection (centre). At Earth, radiation from the flare affects Earth's daytime side (red waves), while the solar wind sculpts the planet's magnetic field into a long 'wind sock' shape. (NASA)

In October 2024, scientists at NASA and NOAA announced that the Sun has entered a period known as solar maximum. This is the peak of the Sun's 11-year solar cycle, when we see the greatest number of sunspots, as well as when the most frequent and powerful solar flares and coronal mass ejections occur.

The current solar cycle, the 25th since record-keeping began in the late 1700s, began in December 2019, when solar activity was at its minimum. Now, over six years later, we are seeing activity at its most intense, and solar maximum is expected to last for at least the rest of 2025. Afterwards, perhaps sometime in 2026, the Sun's activity will begin to diminish again, and scientists will be able to lock down the exact date when it reached its peak for this cycle.

READ MORE: Why are the Northern Lights so supercharged lately and how long will this last?

Some types of solar activity are easily compared to Earthly weather, and this is often reflected in their names.

One example is 'solar wind', the name used for the constant flow of charged particles that escapes the Sun's atmosphere into space. Another is 'solar storm', which is another name for a coronal mass ejection -- the massive clouds of solar particles, weighing in at billions of metric tons, that often erupt from the Sun following a solar flare.

Other phenomena have far more technical names, but still are analogous to weather, such as the 'co-rotating interaction region'. This is the region of the solar wind along the leading edge of a faster, more energetic stream, where high-energy solar particles build up in higher concentrations. Due to both its shape and its tendency to produce more active space weather, the CIR can be likened to an active front on a weather map.

Two panels of NOAA SWPC's ENLIL solar wind computer model are shown here from Feb. 8, 2024, depicting the density of the solar wind (top left) and the speed the solar wind is flowing away from the Sun (top right), as the 'pinwheel' pattern of the solar wind rotates along with the Sun in a counterclockwise direction. The fast-flowing 'coronal hole high speed stream' is labelled, along with the 'co-rotating interaction region' along its leading edge. Bottom centre: a cold front from a weather map is shown, demonstrating the similarities between it and the CIR. (NOAA SWPC/Scott Sutherland)

Overall, though, the term space weather is used to describe any type of solar activity that has impacts here, both to our technologies and to the Earth itself.

Solar flares disrupt long-range radio communications and GPS signals on the day-side of the planet. The stronger the flare, the greater the disruption. Additionally, low-orbiting satellites and spacecraft can experience greater drag due to the heating of the upper atmosphere.

A strong solar flare, shown in extreme ultraviolet from NASA's Solar Dynamics Observatory, is overlaid by the scale scientists use to rank flares. Each letter class is ten times stronger than the class below, with A-class and B-class flares barely discernible, and even C-class going largely unnoticed. M-class flares are more significant, causing minor issues with radio and GPS signals. X-class, the strongest, can cause much more serious issues, and any CME that erupts during the flare often becomes supercharged. While each letter classification from A through M goes from 0-9.9, there is no upper limit to X-class flares. (NASA)

When a co-rotating interaction region or coronal mass ejection sweeps past Earth, their impact distorts and disturbs the planet's geomagnetic field.

This can cause electrical or communication problems in orbiting satellites, power blackouts, such as the one in Quebec in March 1989, and possibly even long-term internet outages due to the effects on the cables that run along the sea floor.

This immense solar prominence tore itself away from the Sun's surface in August of 2012, erupting into a massive coronal mass ejection. According to NASA, "The ejected material did not head directly toward Earth, though some of it did glance off the planet's magnetic environment, or magnetosphere, causing aurora to appear on the night of Monday, September 3." (NASA's Scientific Visualization Studio)

For many people, though, the most visible impacts of space weather are the colourful displays of light in the sky that we call the Aurora Borealis or the Northern Lights.

Auroras occur when high-energy particles from the solar wind or a solar storm are captured by Earth's geomagnetic field and funnelled down into the upper atmosphere. There, the particles collide with and pass on their energy to atoms and molecules in the air. Those atoms and molecules then release that excess energy as coloured bursts of light.

This display of the Northern Lights was captured from Lambton, QC on October 6, 2024. (Alex Dostie/UGC)

Even on 'quiet' space weather days, enough particles are swept up from the solar wind to produce aurora displays near the north and south poles on an almost nightly basis.

However, during more active space weather, especially around solar maximum, auroras can put on extremely bright displays that extend far away from the poles.

These intense auroras often occur during geomagnetic storms.

According to NOAA's Space Weather Prediction Center: "A geomagnetic storm is a major disturbance of Earth's magnetosphere that occurs when there is a very efficient exchange of energy from the solar wind into the space environment surrounding Earth."

As mentioned above, these major disturbances are caused by co-rotating interaction regions and coronal mass ejections. Both of these phenomena are made up of electrically-charged solar particles moving through space, and by one of the fundamental principles of physics, this means that they generate magnetic fields. So, when either a CIR or CME sweeps past us, the magnetic field generated by it interacts with Earth's geomagnetic field, potentially causing a strong reaction.

This reaction is the geomagnetic storm.

The blue lines in this simulation are a simplified representation of Earth's geomagnetic field (aka, the magnetosphere). The pressure of the solar wind flowing past Earth compresses the sunward side (left) of the field, while drawing out the anti-sunward side into a long tail (right). The white spots along the field lines are particles from the solar wind becoming trapped and funnelled into the atmosphere where they produce the Aurora Borealis and corresponding southern Aurora Australis. (NASA)

Magnetic fields not only have strength, but they also point in a specific direction. The strength of the magnetic field along a CIR or inside a CME depends on a few different factors -- the density of the solar particles, the amount of energy carried by those particles, and how quickly they pass by us. However, the direction that the magnetic field points, compared to Earth's geomagnetic field, is typically what determines whether it has an impact in the first place.

Although the magnetic field of a CIR or CME can change direction several times as it passes Earth, any time it points in the same direction as Earth's geomagnetic field, the two fields will repel each other. During these times, the geomagnetic field will divert the flow of particles around us, with little to no impact.

The more the magnetic field of the CIR or CME points opposite to Earth's geomagnetic field, though, the more the two fields will attract one another and actually form connections.

This diagram demonstrates the interaction between a CME's magnetic field and Earth's geomagnetic field, where a CME with a positive field direction is repelled (top), and a CME with a negative field direction is attracted (bottom). Although at Earth's core, the magnetic field is oriented with magnetic north at the geographic south pole, at the surface and out in space, the field is technically oriented opposite to that, with magnetic north pointing towards the geographic north pole. (Javalab/Scott Sutherland)

During this interaction, fluctuations in the geomagnetic field strength, shape, and even direction can generate induced electric currents in orbiting spacecraft, along long-distance power transmission lines, in buried pipelines, and along the internet cables that traverse the ocean floor.

Static charges can build up in satellites to the point where they disrupt computer, communication, and propulsion systems. These currents can also upset the carefully controlled flow of electricity along power lines, disrupt signals along undersea internet cables, and accelerate the corrosion of buried pipelines. The stronger the interaction between the fields, the more intense these induced currents are likely to be, and thus the greater danger to our technologies and power grids.

At the same time, the connections formed between the magnetic fields also open up 'fast tracks' that allow solar particles to stream, en masse, directly from space down into the atmosphere. Additionally, they also effectively peel away the outermost layers of the geomagnetic field, so that the solar particles can interact with the atmosphere farther away from the poles.

This is why Northern Lights displays become more intense during geomagnetic storms, and spread farther south as those geomagnetic storms grow in strength.

In the same way that meteorologists rank hurricanes and tornadoes, forecasters at NOAA's Space Weather Prediction Center rank geomagnetic storms on a scale of 1 through 5. A G1 (minor) geomagnetic storm is the weakest class, while G5 (extreme) is the strongest.

A G1 (minor) geomagnetic storm is often the result of Earth plunging into a fast stream of the solar wind, or when a small, diffuse CME sweeps past, or when a larger, denser coronal mass ejection scores a 'glancing blow' on Earth's geomagnetic field.

According to NOAA, during a G1 (minor) geomagnetic storm, weak power fluctuations can occur in electrical grids, spacecraft can experience minor issues, and migratory animals can be affected (due to their inherent sense of magnetic fields for navigation). Auroras are common at latitudes across northern and central regions of Atlantic Canada, Quebec, and Ontario, and are often visible across the Prairies, typically showing up as displays of green arcs and bands across the sky.

Northern Lights at Keephill, AB. (Brody W./UGC)

For stronger geomagnetic storms to occur (from G2 through G5) this is usually following a more direct impact of a coronal mass ejection. The denser the CME, the more energy the particles in the cloud contain, and the faster the CME sweeps past us, the stronger the impact on Earth's geomagnetic field, and thus the higher the storm will be ranked.

There are also times when the arrival of a CME is timed exactly when Earth crosses into a fast solar wind stream. In that case, the effects from both will combine, ramping up the level of the geomagnetic storm by at least one level above what the CME would have caused on its own.

During a G2 (moderate) geomagnetic storm, NOAA says that power grids at high latitudes may experience voltage alarms, with long-duration storms potentially causing transformer damage. Meanwhile, spacecraft controllers on the ground may need to take action to stop satellites from tumbling, and orbit corrections may be needed. Additionally, high frequency radio transmissions may experience interference from ionospheric effects.

Auroras will intensify, growing brighter and with more red colour showing up in the display. They will also push farther south, covering most of Canada except eastern Newfoundland, Nova Scotia, and southwestern Ontario.

The Aurora Borealis from central Alberta on November 5, 2023. (TeamTanner)

At G3 (strong) geomagnetic storm levels, voltage corrections in power grids may be required, with false alarms being tripped on some devices that protect against overloads. In space, satellites may experience some surface static charging, and upper atmospheric drag could increase, forcing controllers to correct these problems to keep spacecraft in orbit. GPS signals and radio communications may be blocked or experience issues.

Auroras brighten more, the colours intensify, possibly with more purple and blue becoming visible. They extend even farther south than during a G2 storm, covering all of Canada as well as the northern United States.

Aurora from Guelph, ON, on Sept 16, 2024. (Mark Robinson)

G4 (severe) geomagnetic storms are where problems become more serious. Power grids may experience voltage control issues, with sections of the grid losing power as protective systems trip due to the odd current levels on the lines. Spacecraft issues with surface charging, changes in orientation, and atmospheric drag increase. Induced currents may be experienced by underground pipelines, radio and satellite communications could drop out for hours at a time, and radio navigation systems may also experience intermittent problems.

Aurora intensity increases, with displays becoming very colourful. They are often seen overhead from as far south as the central United States, and can even be spotted along the northern horizon from the Gulf Coast states and California.

Auroras spotted from central Alberta, on Nov. 4, 2021. (TeamTanner)

A G5 (extreme) geomagnetic storm is the strongest rank on the scale. Induced currents along power lines can be widespread, possibly causing complete blackouts of entire grids. Some equipment, especially power transformers along the lines, could suffer significant damage. Spacecraft experience more intense surface charging, communication problems, and require corrections from operators on the ground. Pipeline currents can reach hundreds of amps, long-range radio communications may be down for days, while radio navigation is out for hours at time.

This level of geomagnetic storm produces the brightest and most extensive auroras seen in modern times. Colourful displays will fill the skies from northern Canada down to the southern United States. They may even be visible from the Caribbean and across the Gulf of Mexico, along the Yucatan Peninsula.

Northern Lights from central Alberta on March 23, 2023. (TeamTanner)

These ranks are based on measuring geomagnetic activity over 3-hour periods. Any enhanced activity that occurs on a shorter timescale will therefore not be captured on this scale, but may still show up as quick bursts of bright auroras, often referred to as 'substorms'.

NOAA SWPC isn't the only agency that monitors space weather and issues alerts. Natural Resources Canada operates the Canadian Space Weather Forecast Centre (CSWFC) out of Ottawa, where a dedicated team of scientists provide similar geomagnetic and auroral forecasts for the Canadian public.

The CSWFC uses a different five-point system from NOAA's for ranking geomagnetic activity. They also define three different forecast regions: Polar, located north of the Arctic Circle, Auroral, which covers an arc south of the Polar region down to western Labrador, northern Quebec, northern Ontario, central Manitoba and Saskatchewan, northern Alberta, and through northwestern B.C., and Sub-Auroral, which covers the rest of Canada and the northern half of the United States.

This map from Canadian Space Weather Forecast Centre shows a review of geomagnetic activity from February 18-19, 2025, along with the five-point scale used by the Centre to rank activity. The Polar region experienced unsettled conditions (green) with active intervals (yellow stripes), the Auroral region was active (yellow) with stormy intervals (red stripes), and the Sub-Auroral region was unsettled (green) with stormy intervals (red stripes). Regions with consistent levels of activity will show only a solid colour of the appropriate scale level, without the alternate-coloured stripes. (NRCan CSWFC)

At the lowest end of CSWFC's scale is 'Quiet', denoting no expected geomagnetic disturbances or aurora activity. 'Unsettled' and 'Active' conditions represent increasing activity that remains below geomagnetic storm levels. 'Stormy' is the equivalent of a G1 or G2 storm by NOAA's scale, while 'Major Storm' covers conditions equivalent to G3 through G5 geomagnetic storms. Also, since geomagnetic and aurora activity can increase and decrease fairly rapidly, each regional forecast may also include the potential for short intervals of heightened activity, represented by stripes of the appropriate colour.

Based on the scales, forecast periods, and forecast regions they use, comparisons between NRCan CSWFC and NOAA SWPC forecasts will sometimes show significant differences. However, that's generally a good thing.

Space weather impacts can vary quite a bit, and based on the timing, one forecast method might capture conditions better than the other. Checking what both offices are saying, therefore, tends to provide a better perspective on when to look up.