Since October 19, an active region of the sun has been
getting busy. Dubbed AR 12192, the region is the largest sunspot in 24 years --
and most certainly the largest of this solar cycle, which is currently at maximum.
In the space of a week, AR 12192 -- nearly 129,000
kilometres (80,000 miles) across, big enough for 10 Earths to be laid across
its diameter -- has erupted in six massive flares. Five of these flares were
X-class -- the biggest and most powerful class of solar flare. The accompanying
coronal mass ejections -- clouds of electrified gas that explode from the blast
site -- can cause geomagnetic storms and auroras.
The effects of these on Earth include the disruption of
radio and satellite communications and navigational equipment. AR 12192's
flares caused several high-frequency radio blackouts on Earth's dayside, over wide areas for durations of about an
However, unusually, the flares were not accompanied by major CMEs --
which meant no geomagnetic storms and no auroras.
The first flare was observed on October 19, peaking at 1.01
a.m. EDT. At X1.1, it was one of the smallest of the X-class flares. Solar flares
are categorised A, B, C, M and X; each class is ten times as powerful as the previous.
Each class has a smaller scale from 1 to 9; an X2 class flare is
twice as strong as an X1, and an X3 is three times as strong as an X1.
The biggest solar flares don't stop at X9,
though. The strongest solar flare ever seen overloaded the sensors at X28. We don't know precisely how strong it was.