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.
Superflare
Flares are more common in stars with short periods. However, the energy of the largest flares is not related to the period of rotation. Stars with larger variations also have much more frequent flares; there is as well a tendency for them to have more energetic flares. Large variations can be found on even the most slowly rotating stars: one star had a rotation period of 22.7 days and variations implying spot coverage of 2.5% of the surface, over ten times greater than the maximum solar value. By estimating the size of the starspots from the amplitude variation, and assuming solar values for the magnetic fields in the spots (1000 G), it is possible to estimate the energy available: in all cases there is enough energy in the field to power even the largest flares observed. This suggests that superflares and solar flares have essentially the same mechanism.