Solar flares may seem like far-away events,
but they can damage satellites and even ground-based
technologies and power grids. Every 11 years,
as the sun reaches its maximum activity they
become bigger and more common, and that increases
the chances that one will significantly affect
Earth.
So what are these solar eruptions? A solar
flare is basically an explosion on the surface
of the sun ranging from minutes to hours in
length. Large flares can release enough energy
to power the entire United States for a million
years. Flares happen when the powerful magnetic
fields in and around the sun reconnect. They're
usually associated with active regions, often
seen as sunspots, where the magnetic fields
are strongest.
Flares are classified according to their strength.
The smallest ones are B-class, followed by
C, M and X, the largest. Similar to the Richter
scale for earthquakes, each letter represents
a ten-fold increase in energy output. So an
X is 10 times an M and 100 times a C. Within
each letter class, there is a finer scale
from 1 to 9. C-class flares are too weak to
noticeably affect Earth.
M-class flares can cause brief radio blackouts
at the poles and minor radiation storms that
might endanger astronauts. It's the X-class
flares that are the real juggernauts. Although
X is the last letter, there are flares more
than 10 times the power of an X1, so X-class
flares can go higher than 9. The most powerful
flare on record was in 2003, during the last
solar maximum. It was so powerful that it
overloaded the sensors measuring it. They
cut out at X17, and the flare was later estimated
to be about X45.
A powerful X-class flare like that can create
long lasting radiation storms, which can harm
satellites, and even give airline passengers
flying near the poles small radiation doses.
X flares also have the potential to create
global transmission problems and worldwide
blackouts.
The seriousness of an X-class flare pointed
at Earth is why NASA and NOAA constantly monitor
the sun. NASA's Heliophysics fleet of spacecraft
can now see the sun from every side and in
many different wavelengths. This unprecedented
coverage is enabling scientists to predict
and detect space weather events like flares
and CMEs with ever greater accuracy. With
advance warning, governments and companies
can take steps to protect their technological
infrastructure, so that the worst scenarios
will never happen.
