Coronal Mass Ejections
A coronal mass ejection, or
CME, for short, is an ejection of large amounts of matter from
the sun’s atmosphere,
or corona. One of the most spectacular displays of solar activity,
CMEs can fling into space billions of tons of solar material, called
plasma, as well as embedded magnetic fields. The ejected material
hurdles into space at speeds up to several million miles per hour,
creating an interplanetary shock wave.
CMEs are thought to arise from large-scale
magnetic instabilities. The solar atmosphere is contained by
magnetic fields that can suddenly rearrange, releasing an enormous
bubble of matter—a coronal
mass ejection. CMEs are sometimes (but not always) associated with
We are able to see CMEs thanks to a special type of telescope
called a coronagraph. Ordinarily, the bright light of the sun drowns
out most of the detail of the corona. A coronagraph gets around
this problem by creating an artificial eclipse. A circular shade
in the middle, called the occulting disk, blocks out the bright
sun so the corona can be seen.
You can spot CMEs on a coronagraph image as a
large white tongue, blob, or halo that erupts from the corona.
CMEs that are pointed toward earth are called halo events, because
the approaching matter seems to surround the sun like a halo. Traveling
at an average speed of a million miles per hour, a halo-event CME
generally reaches the earth in two to four days, where it may cause
a geomagnetic storm.
for CMEs using live data
a movie of
over the last few days
movie of the
October 2003 event