Astro Bob: Solar Cycle 25 is on a hot streak
Flares and sunspots have been more frequent than predicted in the current solar cycle, offering an optimistic outlook for auroras in the next few years.
It wasn't just my imagination. Sunspot and solar flare activity have ticked up more quickly than anticipated in the past year. We know our star has its ups and downs. About every 11 years, sunspot numbers and solar storms peak, then fade and disappear before cresting again. Each cycle is numbered; the first, called Solar Cycle 1 commenced in February 1755 and ended in June 1766. We're now into Solar Cycle 25, which began in December 2019 and is predicted to reach maximum in July 2025.
Sunspot groups are manifestations of powerful magnetic fields and have magnetic poles just like magnets — positive and negative. During one cycle, the leading spot will be the positive pole, and the following spot (or spots) the negative pole. When a new cycle begins, the poles switch, and the lead spot becomes negative and the follower positive. Astronomers can pinpoint the start of a new cycle by identifying the first spots that show this reversal .
Back in the fall of 2020, the Solar Cycle 25 Prediction Panel, an international group of experts co-sponsored by NASA and NOAA, announced their prediction for the current solar activity cycle. Based on observed trends they predicted a fairly weak cycle similar to the previous one. But the sun has so far defied those projections. Instead, sunspot numbers, according to the Spaceweather website, have "exceeded predictions for 15 straight months."
Take a look at the graph. It plots monthly sunspot numbers against time. The red curve is the prediction. You'll notice that soon after minimum, the monthly sunspot count (black dots) run higher than expected and then really take a leap in late 2021. In December, the predicted monthly sunspot number was 27, but the actual number was 68, more than twice the forecast. The last time the sun was this speckled was back in 2015.
Around solar minimum, the sun can be spotless for many weeks. But in a sign of good things to come, the year 2021 saw just 64 spotless days and nearly three times as many geomagnetic storms compared to 2020.
If the trend continues, Cycle 25 might be a barn burner or at least better than "weak." Powerful flares and coronal mass ejections have a good side and a bad side. Big storms can threaten poorly protected power grids and damage sensitive satellite electronics. On the flip side, they often lead to more frequent and intense northern and southern lights. Yeah, we'll take that.
Then there's the joy of observing sunspots.. No need to drive anywhere for dark skies. Just set up a telescope (covered with a safe solar filter, of course!) in the sunshine. At first glance, sunspots look like dark bugs on the sun's face, but a closer look reveals their two-part structure. Larger spots exhibit a dark core called an umbra encircled by pale, outer fringe with a cross-hatched texture called the penumbra.
As the sun rotates, the sunspots go along for the ride and take about four weeks to make a complete spin. Most groups are gone by the next rotation, but some can last up to about 100 days. Their appearance changes constantly as they grapple with the turbulent and super-hot solar surface which sizzles at around 10,000° F (5,500° C). Sunspots are several thousand degrees cooler than their surroundings, which makes them look dark in comparison. In truth, they would shine brilliantly if we could see them separate from the sun.
Powerful magnetic fields within sunspot groups temporarily insulate them from the superheated plumes of incandescent hydrogen gas bubbling up from below. Oodles of energy stored in those fields are sometimes released in mind-boggling explosions called solar flares. This week (Jan. 10-16), at least four groups are visible in small telescopes fitted with a proper solar filter .
My friend David has been sketching sunspots for decades. His careful work has sharpened his eye for detail as well as deeply informed him of the sun's volatility. Watching an astronomical object change is exciting and gratifying experience, whether it be cloud patterns on Jupiter, the light pulsations of a variable star or checking the sun's pulse through its spots.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at