Big Sunspot Group Has Flare Potential

The sunspot group AR2778 is the largest of the new solar cycle. This photo was taken by NASA's Solar Dynamics Observatory (SDO) late Wednesday morning, Oct. 28. NASA / SDO

The largest sunspot group of new Solar Cycle 25 is getting out attention this week. If you have a small telescope equipped with a safe solar filter, take a look. Although the individual sunspots are only modest-sized, the group as a whole extends across 62,000 miles (100,000 km). Its official name is Active Region (AR) 2778. 

The sun isn't a rigid body like the Earth but spins at rates that vary with latitude. NASA

Because the sun turns on its axis from east to west about once every 27 days, the sunspot group moves further to the west each day. It's currently in the southwestern part of the disk, so we have a few more days of observation before it rotates around to the backside. Notice I used the word "about" when describing the sun's rotation period. Unlike the rigid Earth, our star is a ball of hot, compressed gas called plasma and spins at different rates depending upon latitude.

This image of the sun made today maps the intensity of magnetic fields on its surface and clearly shows the "poles" of sunspot group 2778. One end of the group (white) has a positive polarity — like one pole of a magnet — and the other has a negative polarity. NASA / SDO

At the equator one rotation takes just 24 days while at the poles it takes more than a month! Differential rotation causes magnetic fields within the sun to "wind up" and intensity over time, then rise to the surface and manifest themselves as sunspots. Most sunspot groups have a north pole at one end and a south pole at the other just like a common bar magnet. 

Photographed in ultraviolet (UV) light, AR2778 reveals loops of magnetic energy that constrain plasma (ionized gas) in the sun's atmosphere much like iron filings sprinkled around a bar magnet reveal the contours of its otherwise invisible magnetic field. NASA / SDO

Sunspots are dark because their concentrated magnetic energy keeps them cooler than the surrounding area, making them appear dark in contrast. Sometimes that energy can build to great intensity, giving rise to solar flares which can spark displays of the aurora as well as disrupt radio communications and potentially damage satellite electronics. Everyone from northern lights watchers to power and telecommunication companies have an interest in what the sun is up to.

We're currently in Solar Cycle 25 which is predicted to peak in July 2025 with a maximum sunspot number of 115. NASA / NOAA

AR2778 is a member of the current solar cycle. The previous cycle, Solar Cycle 24, finished up when it reached minimum (a lull in solar activity) in December 2019. The last cycle was typical in length at 11 years but had the 4th smallest intensity since regular record keeping began with Solar Cycle 1 in 1755. Solar Cycle 25 is expected to peak in 2025 and mimic the humdrum performance of the previous cycle. 

AR2778 has a more complex magnetic field than a simple sunspot group with the potential to produce flares. Should one occur today, it would be "geoeffective" because the group is facing toward the Earth. Particles shot out by a flare would potentially fire up auroras in a couple of days. Like getting a pie in the face. Bring it on!