Mystery at the Sun's South Pole
Nasa reveals huge 'coronal hole' on the solar surface where winds reach 500 miles per SECOND
By Mark Prigg
Daily Mail
Daily Mail
January 5, 2015
However, the sun has started 2015 with a mysterious event – a huge hole has appeared.
Known as a coronal hole, the phenomenon
occurred near the south pole – and is seen as a dark area covered all of
its base in these stunning images.
The incredible image was captured on Jan.
1, 2015 by the Atmospheric Imaging Assembly (AIA) instrument on NASA’s
Solar Dynamics Observatory, shows the coronal hole as a dark region in
the south.
Coronal holes are regions of the corona
where the magnetic field reaches out into space rather than looping back
down onto the surface.
Particles moving along those magnetic
fields can leave the sun rather than being trapped near the surface.
Those trapped particles can heat up and glow, giving us the lovely AIA
images.
In the parts of the corona where the particles leave the sun, the glow is much dimmer and the coronal hole looks dark.
Coronal holes were first seen in images taken by astronauts on board NASA’s Skylab space station in 1973 and 1974.
They can be seen for a long time, although the exact shape changes all the time.
The polar coronal hole can remain visible for five years or longer.
Each time a coronal hole rotates by the
Earth we can measure the particles flowing out of the hole as a
high-speed stream, another source of space weather.
Charged particles in the Earth’s radiation belts are accelerated when the high-speed stream runs into the Earth’s magnetosphere.
The acceleration of particles in the magnetosphere is studied by NASA’s Van Allen Probes mission.
As Solar Cycle 24 fades, the number of
flares each day will get smaller, but the coronal holes provide another
source of space weather that needs to be understood and predicted.
Coronal holes are a typical feature on the
sun, though they appear at different places and with more frequency at
different times of the sun’s activity cycle.
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