Explanation:
The dark expanse below the equator of the Sun is a
coronal hole --
a low density region extending above
the surface
where the solar magnetic field opens freely into
interplanetary space.
Shown in false color,
the
picture was recorded on September 19th
in extreme ultraviolet light by the
EIT
instrument onboard the space-based SOHO observatory.
Studied extensively
from
space since the 1960s in ultraviolet
and x-ray light,
coronal holes are known to be the source of
the high-speed solar wind, atoms and electrons
that flow outward along the open
magnetic field lines.
The solar wind streaming from this coronal hole
triggered colorful
auroral displays on
planet Earth begining late
last week,
enjoyed by spaceweather watchers at
high latitudes.
