Solar Activity

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Solar Activity
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The Sun Ever Changing
The Sun is a variable star. Here, we concentrate
on the Solar Activity Cycle.
The principal manifestation of the Solar Activity
Cycle is the changing number of sunspots visible
on the surface of the Sun.
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Sunspots
Chinese Records of sunspot observations in
China go back to at least 28 BC. Galileo
discovered solar mountains? Holes? It is
possible that the Greek philosopher Anaxagoras
observed a spot in 467 BC, and it appears that
there are a few scattered mentions in the ancient
literature as well.
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What do we know?
We know they are areas of cooler gas 4000K.
Why darker? Because cooler than the surrounding
gas and they give off less intense amounts of
light because of this cooler temperature.
Also sunspots have very large magnetic
properties. They always seem to appear in
magnetic (N/S) pairs.
As discovered in 1843 by Heinrich Schwabe, a
German apothecary, the number of Sunspots varies
roughly periodically with a period of 11 years
(The cycle based on other markers suggests that
the period is actually 22 years.)
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This striking close-up of AR9077 was made by the
orbiting TRACE satellite shortly after the flare
erupted. It shows million degree hot solar plasma
cooling down while suspended in an arcade of
magnetic loops. Collectively resembling a
"slinky" toy, the enormous loops are actually
magnetic field lines which trap the glowing,
cooling gas. Active regions like AR9077 appear as
groups of dark sunspots in visible light.
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11 Year Cycle
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Sunspot Locations?
In addition to the variation in the number of
sunspots, their location on the surface of the
Sun changes over the sunspot cycle. As the
activity level of the Sun increases the sunspots
appear closer to the equator of the Sun.
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Solar Activity Cycle Cycles?
Based on the historical record, it has been shown
that the Sunspot Cycle can stop, that is, there
are stretches where there are no visible
Sunspots. There have been several such intervals
in recent history. The most prominent one is
referred to as the Maunder Minimum which occurred
in the 1600's.
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Maunder Minimum
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Whats going on?
What is the prevailing theory as to what is
causing these sunspot variations?
Magnetic Fields!
Solar Rotation
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Differential Rotation
Since the Sun is not a solid object, it rotates
much more like a liquid. As the Sun rotates on
its axis it does not carry all parts of itself
around equally. In fact, there is differential
rotation. That is to say, the equator material
rotates once around the Suns axis more quickly
than material progressively farther away from the
equator.
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Babcock Model
The Babcock Model theorizes that the differential
rotation of the Sun winds up the magnetic fields
of is layers during a solar cycle. The magnetic
fields will then eventually tangle up to such a
degree that they will eventually cause a magnetic
break down and the fields will have to struggle
to reorganize themselves by bursting up from the
surface layers of the Sun. This will cause
magnetic pair boundaries (spots) in the
photosphere trapping gaseous material that will
cool slightly. Thus, when we see sunspots, we are
seeing these areas of magnetic field breakdown.
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