One, dubbed active region 1890, produced considerable solar activity in the past weeks including several mid-sized and significant flares, but has almost rotated off completely and will soon be out of sight from Earth, they said.
The newer active region, 1897, came into view Monday and is now making its way across the Earth-side of the sun, NASA reported.
An active region can contain one or more sunspots, astronomers said.
Increased numbers of sunspot active regions and their associate flares are quite common at the moment, as the sun approaches the peak of its normal 11-year activity cycle, constantly tracked since the cycle was discovered in 1843.
During the sun's peak activity, called solar maximum, it is normal to record many flares a day, the astronomers said.