Prominences
and plages
are structures that occur above the photosphere of the
Sun.
Plages are bright cloud-like features found around sunspots
that represent regions of higher temperature and density within the chromosphere.
Prominences are features that may reach high into the corona, often as
graceful loops that may hang suspended for many days.
Solar Prominences
The right image shows an eruptive prominence recorded by SOHO on June 14, 1999
(Ref).
South is up in this image, which is recorded in the extreme UV part of the spectrum in
the light of ionized helium atoms.
The left image below shows a prominence on the edge of the Sun
photographed in H-alpha light
by the Big Bear Solar Observatory at 16:17 UT on October 3rd, 1996
(Ref).
The right image below shows a total solar eclipse, with several prominences in red
on the limb of the Sun.
The bright red color of prominences is associated with strong emission of Balmer
H-alpha radiation.
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Prominence on the solar limb.
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Prominences visible during a total solar eclipse.
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Quiescent prominences
are extremely stable features and remain suspended in the
corona where they slowly evolve
and become more elongated over the course of several solar rotations (a timescale
of a few months).
The loops in the prominence shown in the following image are larger than the
Earth, which would easily fit under them.
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A large solar prominence
(Ref)
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Prominences can also appear as eruptive phenomena, with the highest velocities
observed as fast as 1300 km/second, and have been observed to reach heights of 1
million kilometers above the photosphere.
Prominences and Magnetic Fields
Prominences are usually associated with regions of sunspot activity, and are
clearly associated with the Sun's magnetic field. They tend to lie on the
boundary of regions having opposite magnetic polarity.
The streaming arches and their
stability for days at a time are associated with magnetic forces acting on the
charged particles in the loops. It is thought that the violently eruptive
prominences that are sometimes observed are associated with corresponding sudden
changes in the magnetic field of the Sun.
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Plage clouds
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Solar Plages
Plages are particularly visible when photographed through filters passing the
spectral light of hydrogen or calcium. The adjacent image shows plages near
a sunspot (the white cloud-like feature)
as imaged by the Big Bear Solar Observatory
(Ref).
