A large active region on the sun, an area consisting of intense and complex magnetic fields, came into view on October 18, 2014. The region, labeled AR 12192, quickly grew to the largest such region in 24 years, firing off 10 sizable solar flares as it made its way across the face of the sun. The region’s expansive size allowed it to be seen without a telescope for anyone viewing the sun with eclipse glasses, which many did during the sun’s partial eclipse on October 23.

Alex Young, solar scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in a statement, “Despite all the flares, this region did not produce any significant coronal mass ejections.” Coronal mass ejections, or CMEs, are large clouds of solar particles that can affect technology when they reach space close to Earth. Young continued, “You certainly can have flares without CMEs and vice versa, but most big flares do have CMEs. So we’re learning that a big active region doesn’t always equal the biggest events.”

These active regions are measured in millionths of a solar hemisphere, where 1 micro-hemisphere, or MH, equals approximately 600,000 square miles. The region reached 2,750 MH, making it the 33rd biggest region out of roughly 32,000 active regions that have been tracked and measured since 1874. The sunspot is the largest one seen since AR 6368, which measured 3,080 MH on November 18, 1990. The largest five active regions ever appeared between 1946 and 1951, and were between 4,000 and over 6,000 MH.

According to exploratorium.edu, sunspots can be as large as 50,000 miles in diameter, contracting and expanding as they move across the sun’s surface.