Solar eruptions pushed the northern lights toward the northern U.S. this week

A series of eruptions on the sun’s surface sent bursts of charged particles toward Earth this week, arriving with enough force to push the aurora borealis unusually far south into the northern United States. Skywatchers across states that rarely see the display got a chance to catch faint bands of green and red light low on the northern horizon as the storm reached its peak.

Coronal mass ejections en route to Earth

The activity traces back to coronal mass ejections, enormous clouds of magnetized plasma that the sun periodically hurls outward from active regions on its surface. Multiple eruptions launched material toward Earth in early September, and the leading edge of that plasma reached the planet’s magnetic field around September 8, arriving roughly two to three days after the eruptions were first observed, the typical transit time for a fast-moving ejection crossing the roughly 93 million miles between the sun and Earth.

When a coronal mass ejection strikes Earth’s magnetosphere, it compresses and disturbs the field, funneling charged particles down toward the poles where they collide with oxygen and nitrogen molecules in the upper atmosphere and produce the glowing curtains of light known as the aurora. According to a report from Daily Galaxy, the eruptions behind this week’s display were significant enough to generate a measurable geomagnetic disturbance rather than the fainter fluctuations that pass largely unnoticed outside of scientific instruments.

A G1 storm with G2 potential

Space weather agencies classify geomagnetic storms on a five-step scale running from G1, the mildest, to G5, an extreme event capable of disrupting power grids and satellite operations. The incoming eruptions were expected to produce a G1, or minor, storm, with forecasters flagging the possibility that conditions could briefly intensify to G2, a moderate classification.

Even a G1 storm can push the aurora’s typical viewing boundary, which usually sits across Canada and Alaska, several hundred miles farther south, while a G2 storm can extend visibility into a wider band of northern-tier states on a clear night. The difference between the two classifications often comes down to the orientation of the magnetic field embedded in the incoming plasma, a detail that can shift the storm’s intensity even when its overall speed and density were predicted accurately in advance.

How NOAA tracks the storm in real time

The National Oceanic and Atmospheric Administration’s Space Weather Prediction Center maintains the primary U.S. system for monitoring geomagnetic activity, drawing on satellites positioned between the sun and Earth to detect incoming plasma before it arrives and to measure the storm’s strength once it does. The agency’s aurora dashboard translates that data into a forecast of how far south the lights are likely to be visible on a given night, updating as new measurements come in from the approaching solar material.

That kind of real-time tracking is what allows forecasters to narrow a storm’s likely intensity and timing within a window of hours rather than days, since the exact strength of a coronal mass ejection often cannot be confirmed until instruments positioned roughly a million miles from Earth register its arrival. Earlier estimates based on how the eruption looked leaving the sun can shift once the plasma is actually measured passing that monitoring point.

Where the aurora became visible

Auroral displays tied to G1 and G2 storms typically favor states along the Canadian border and the upper stretches of the northern U.S., including parts of the Dakotas, Minnesota, Wisconsin, Michigan’s Upper Peninsula, and northern New England, though visibility depends heavily on clear skies and minimal light pollution. Observers farther from cities and away from a bright moon generally have the best chance of picking out the display, particularly since a minor storm’s aurora tends to appear as a subtle glow rather than the vivid, rapidly shifting curtains associated with the strongest geomagnetic events.

Photographs taken with longer camera exposures often reveal color and structure in the sky that is difficult to see with the naked eye during a moderate storm, a gap between what a camera sensor can gather over several seconds and what the human eye perceives in real time. That gap has made smartphone night-mode cameras an increasingly common tool for confirming a faint display that might otherwise go unnoticed by someone glancing at the horizon.

The atmospheric chemistry behind the colors

The aurora’s palette comes from which atmospheric gas the incoming particles strike and at what altitude. Oxygen atoms produce the familiar green glow at lower altitudes, the color most commonly reported during minor and moderate storms, while oxygen at higher altitudes can generate a rarer red hue. Nitrogen molecules contribute blue and purple tones, usually appearing along the lower fringes of a display where the atmosphere is denser.

The specific mix of colors visible during any given storm depends on the energy of the incoming particles and how deep into the atmosphere they penetrate, which is part of why a G1 storm and a G5 storm can look markedly different even when both technically qualify as an aurora. Stronger storms tend to push the display lower in altitude and farther in latitude, which is part of why the most intense geomagnetic events can produce vivid color visible even from cities, while a minor storm like this week’s usually rewards only those who seek out a dark, unobstructed view of the northern sky.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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