Bell Tone
Bell Tone
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Narrator: When we look up at the sun from Earth, it seems calm and unchanging.
The truth is quite different.
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In addition to these abrupt changes in activity, the sun also has long
term, more regular pattern of change. This pattern is called the sunspot
cycle and a single cycle lasts for about 11 years, although it can be as short
as 8 or as long as 14 and it can vary dramatically in intensity.
During one cycle, the number of sunspots, a good indicator of 
solar activity, goes from low to high and back down to low.
Solar minimum represents a time when sunspot numbers are relatively low,
and solar maximum represents a period when sunspot numbers are relatively high.
During this cycle, the location of the sunspots also
changes. They are at middle latitudes during solar maximum, and move
closer to the equator as the sun approaches solar minimum. At solar minimum,
there are sometimes no sunspots to observe. At solar maximum there can be many
at the same time. The number of sunspots is important
because sunspots are the visual markers of where powerful magnetic fields have emerged
from the sun's interior. These magnetic fields power solar flares and 
coronal mass ejections, which can affect Earth and other objects in the solar system.
As the sunspots increase, so does the frequency and severity
of flares and CMEs. The sun's 11-year
cycle is a symptom of a longer, 22-year-cycle called the solar cycle,
or Hale Cycle, which affects the sun's magnetic fields.
Every 11 years, the sun's poles flip--north becomes south and south
becomes north, so every 22 years, the poles return to the position
where they started the cycle. The flip is due to the complex movement of
magnetic fields inside the sun that are constantly stretching, twisting, and 
crossing as solar material bubbles up from the sun's core. But the exact
pattern of movements is not yet mapped out. Because the sunspot
cycle follows a similar pattern regardless of the orientation of the poles,
it only takes half as long as the solar cycle. The two cycles are different,
but the 11-year sunspot cycle is often referred to as the solar cycle,
which can be a little confusing. Right now the
sun is approaching solar maximum, so flares and CMEs are more common than
they were a few years ago. This cycle may peak in 2013, or
early 2014, and should reach its minimum around 2020
although predictions about the sun are still uncertain. The slower
than expected progress of this sunspot cycle has led some to speculate
that the next sunspot cycle might be very minimal, with few sunspots even at
solar maximum. It is still far too early to know, but even if this is
the case, it has happened before and isn't something to worry about, it just means
that the sun would briefly be a little closer to the unchanging orb it looks like from
the ground.
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