The surface of the Sun
is a very cold place. When compare it with the crown, the upper atmosphere of
the Sun, which is almost 400 times hotter. This large temperature difference has
long been a mystery, but a newly discovered feature in the Sun's magnetic field
could help us get to the bottom of it.
The Sun's magnetic
field tangled includes huge loops forming an arc from the surface to the crown.
We can see the bright loops because the surface plasma flows along its curves.
Richard Frazin of the
University of Michigan, Ann Arbor, and his team measured the temperature of
coronal loops during solar minimum, a period in which they are quiet fewer
sunspots and flares. They hoped that all loops were warmed with height, since
that was the case in the measurements made during the most active phases.
Surprisingly, some of
the loops near the Sun Ecuador cooled closer to their tops. Frazin believes
these "small loops" recently discovered there throughout the solar
cycle and can be an indication of what it is that causes coronal heating. Clare
Parnell of the University of St. Andrews, UK, agrees that small loops are a new
factor that any model must include solar heating.
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