Since the start of last year, folks around the Valley have been incredibly spoiled to see the Northern Lights in the nighttime sky. Most recently seen earlier this year, the spectacle is typically limited to the high latitudes, rather than places as far South as our area.

 

 

The cherry on top was an event in May 2024, where a G5 Geomagnetic storm (the highest classification possible) brought aurora conditions all the way south into Mexico. This was the largest solar storm in about 20 years, and the first time in a very long time that these lights were as vivid as they were. Another event later that year wasn’t as vivid, though these two in quick succession were a major stray from typical Northern Lights activity. 

To understand why the aurora borealis, or northern lights, have been visible so frequently, let’s figure out what goes on where it originates: the Sun.

 

 

If you were to look at the sun with the naked eye, it would be hard to discern anything other than a bright, yellow orb. Removing the “glare”, however, can reveal dark, pimple-like circles called sunspots. These are dark areas at the Sun’s photosphere coming from magnetic flux pushing up from within the solar interior. These spots are about 3,000 degrees cooler than the surrounding area and can come and go over vast timescales. Some can change in hours, while others can last for months. Changes in the alignment of sunspots can cause significant space weather events, such as coronal mass ejections (CMEs), which will be discussed in a moment.

 

 

It is important to note that sunspots are part of a greater solar cycle. Lasting about 11 years, each cycle describes the changing amount of sunspots within the star. At the cycle’s minimum, very few new sunspots form each day. However, at the maximum, hundreds of independent spots can form on the surface of the sun each day. Erratic solar activity is most favored during the maximum stage of each cycle.

Several CMEs occur each day during the solar maximum. CMEs eject a significant amount of plasma mass from the Sun’s Corona to its Heliosphere- the two outer layers of the star. If the CME is strong enough to enter outer space, it can travel to Earth’s magnetosphere, or the planet’s magnetic field. Particles can enter the atmosphere through the poles, where the magnetosphere is at its weakest, causing auroras at higher latitudes.

 

 

As it turns out, the Sun is currently at a solar maximum. Scientists have numbered these cycles since the 1800s. The current one, solar cycle 25, began in December 2019 and has overperformed expectations. This one is also coming off an underperforming solar cycle 24, which peaked in 2014. That cycle was the least active stretch on record, and sparked some discussions among scientists that the Sun may be entering a prolonged quiet period. With a “lull” period thanks to an underperforming previous cycle, last May’s geomagnetic storm ended up being the largest solar storm since the previous peak back in the early 2000s.

The combination of an unexpectedly strong current solar cycle and an unusually weak previous cycle has caused the most recent solar events to stand out.