The northern lights may be visible this weekend after the sun appeared to wake from a slumber.
Solar activity reached high levels, with five M-class solar flares on the sun on Thursday, April 23, which were followed by a rarer X2.4-class event on Friday, April 24.
An eruption of electromagnetic radiation in the sun’s atmosphere, a solar flare is caused by twisted magnetic fields, typically above sunspots — cooler, darker regions of the sun’s surface that form when clumps of its magnetic field well up from deep within the sun.
It’s too early to say exactly what the effects may be, but NASA’s orbiting Solar Dynamics Observatory tracked a coronal mass ejection (CME) — a cloud of super-charged particles — traveling in the direction of Earth in the wake of one of the M-class flares. It also caught comet C/2025 R3 (Pan-STARRS) in its images as it approaches the sun — due to get closest on April 27.
According to Spaceweather.com, a G1-class geomagnetic storm is possible on Sunday, April 26, when the CME may graze Earth’s magnetic field.
More solar flares are likely on Friday, April 26, and through the weekend. “Isolated G1 (Minor) geomagnetic storming conditions are possible on April 26 in response to the arrival of the glancing CME impact,” stated a space weather forecast from the National Oceanic and Atmospheric Administration.
What Causes The Northern Lights
Solar flares don’t cause auroras. Traveling at the speed of light, radiation from a solar flare takes minutes to reach Earth. The northern lights are caused by the solar wind, a constant stream of charged particles flowing from the sun that interacts with Earth’s magnetic field. While most are deflected, some particles spiral along magnetic field lines toward the poles, colliding with oxygen and nitrogen atoms high in the atmosphere. These collisions excite the gases, causing them to release energy as shimmering light.
The root cause of geomagnetic disturbances is CMEs, which often follow a solar flare. During a CME, a cloud of super-charged particles leaves the solar surface and travels across the solar system, though at a much slower speed than the radiation from a solar flare.
Forecasting The Northern Lights
The aurora borealis is notoriously difficult to predict. That’s because it’s very difficult to know whether a CME is Earth-bound and, if it is, exactly when it will arrive. After all, there are no satellites close to the sun to detect the speed of a CME. That data can only be collected when the CME’s effect on the solar wind — the stream of charged particles released from the sun that travels in all directions in the solar system — is measured by NOAA’s DSCOVR satellite, which orbits Earth. DSCOVR measures the solar wind’s speed and magnetic intensity, which is critical in calculating how it is about to change. Only then can an aurora display be accurately forecast by NOAA’s Space Weather Prediction Center, but there’s not much warning — just 30 minutes.
A Waning ‘Solar Maximum’
The sun has a roughly 11-year cycle in which its magnetic activity peaks and troughs. How active it is is measured by counting sunspots on its surface, dark patches that indicate complexity — and often produce solar flares and CMEs. NASA and NOAA’s Solar Cycle 25 Prediction Panel announced the arrival of solar maximum in October 2024, though the exact date won’t be obvious for a few years.
However, the declining phase of the solar maximum can see extreme solar events. Even when the number of sunspots begins to decrease, big displays of aurora are possible.
Solar Cycle 25’s Most Powerful Solar Flares
Although an X2.4-class solar flare is the biggest for months, there have been much stronger events in the current solar cycle:
- Oct. 3, 2024 — X9 (the strongest of solar cycle 25, which caused global auroras).
- May 5, 2024 — X8.7
- Oct. 1, 2024 — X7.1
- Feb. 22, 2024 — X6.3
- May. 11, 2024 — X5.9 (caused global auroras).
Solar flares are graded according to their severity, with B-class, followed by C, M and X, according to NASA. Each letter represents a tenfold increase in energy output. The strongest ever solar flare detected was an estimated X28 on Nov. 4, 2003.
Northern Lights Updates
Aurora-chasers frequently use the Kp index to predict the intensity of a geomagnetic storm, but for aurora displays, the interplanetary magnetic field’s Bz component is more important. Bz determines how easily solar energy enters Earth’s magnetosphere. When Bz points north, Earth’s field resists it; when Bz swings south, the two fields connect, allowing plasma to stream in. A sustained southward Bz of −5 nT or stronger usually signals an imminent display of aurora.
To check visibility in real time, use NOAA’s 30-minute aurora forecast or download apps such as Aurora Now, My Aurora Forecast or Glendale Aurora for up-to-the-minute alerts and live solar wind data.
Wishing you clear skies and wide eyes.
