Solar flare
Other large solar flares also occurred on April 2, 2001 (X20), October 28, 2003 (X17.2 and 10), September 7, 2005 (X17), February 17, 2011 (X2), August 9, 2011 (X6.9), March 7, 2012 (X5.4), July 6, 2012 (X1.1). On July 6, 2012, a solar storm hit just after midnight UK time, when an X1.1 solar flare fired out of the AR1515 sunspot. Another X1.4 solar flare from AR 1520 region of the Sun, second in the week, reached the Earth on July 15, 2012 with a geomagnetic storm of G1–G2 level. A X1.8-class flare was recorded on October 24, 2012. There has been major solar flare activity in early 2013, notably within a 48-hour period starting on May 12, 2013, a total of four X-class solar flares were emitted ranging from an X1.2 and upwards of an X3.2, the latter of which was one of the largest year 2013 flares. Departing sunspot complex AR2035-AR2046 erupted on April 25, 2014 at 0032 UT, producing a strong X1.3-class solar flare and an HF communications blackout on the day-side of Earth. NASA's Solar Dynamics Observatory recorded a flash of extreme ultraviolet radiation from the explosion. The Solar Dynamics Observatory recorded an X9.3-class flare at around 1200 UTC on September 6, 2017.
Barnard's Star
In 1998 a stellar flare on Barnard's Star was detected based on changes in the spectral emissions on 17 July during an unrelated search for variations in the proper motion. Four years passed before the flare was fully analyzed, at which point it was suggested that the flare's temperature was 8000 K, more than twice the normal temperature of the star. Given the essentially random nature of flares, Diane Paulson, one of the authors of that study, noted that "the star would be fantastic for amateurs to observe".
The flare was surprising because intense stellar activity is not expected in stars of such age. Flares are not completely understood, but are believed to be caused by strong magnetic fields, which suppress plasma convection and lead to sudden outbursts: strong magnetic fields occur in rapidly rotating stars, while old stars tend to rotate slowly. For Barnard's Star to undergo an event of such magnitude is thus presumed to be a rarity. Research on the star's periodicity, or changes in stellar activity over a given timescale, also suggest it ought to be quiescent; 1998 research showed weak evidence for periodic variation in the star's brightness, noting only one possible starspot over 130 days.