In mid-May, a historic geomagnetic storm streaked 100 kilometers overhead, causing the Northern Lights to blanket skies around the world for several nights. While it was likely a once-in-a-lifetime experience to see the Northern Lights deep in the tropics, an even more powerful geomagnetic storm is almost certain to occur later this year, raising hopes for aurora watchers around the world that even more dazzling lights may be on the horizon.
That’s because the sun is rapidly approaching a solar maximum, a predictable 11-year peak in activity. Solar flares and coronal mass ejections (CMEs) often occur during and immediately after solar maximum and are what cause the vibrant auroras.
The Great Aurora Show on May 10, 2024 was caused by three CMEs that erupted from the Sun’s outer atmosphere and headed towards Earth. A CME is a collection of magnetized plasma ejected from the Sun’s extremely hot outer atmosphere, the corona, as a result of a disturbance in the Sun’s magnetic field.
On May 10, successive CMEs, each moving slightly faster than the previous, merged into three bursts of charged particles before blanketing Earth’s atmosphere. As the three CMEs struck Earth simultaneously, their combined energy created a historic auroral spectacle.
AR3664 on May 10, 2024.Photo: NASA/SOHO
These CMEs are associated with Active Region 3664, a collection of relatively cool, dark sunspots on the Sun’s surface that has grown to more than 15 times the size of the Earth itself. View AR3664 without zoom All you have to do is look at the sun through eclipse glasses.
It turns out that the sheer size of AR3664 was a major contributor to this generation of auroral events. Such spots on the Sun’s surface often disrupt the local magnetic field, causing instability and rearrangements that can trigger CME emissions and powerful solar flares that can cause radio interference.
Because the surface of the Sun rotates on its axis approximately every three and a half weeks, sunspots are only visible from Earth for one or two weeks, depending on where on the Sun’s surface they form.