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Aubrey Weese
English 301-N01
Explaining Science Using Examples - Final Revision
Changes in the magnetic field of the sun affect us here on earth in a number
of interesting ways. This
magnetic field
is caused by the flow of electrically charged ions and electrons on the sun,
and if it didn't exist, the sun would be a much more boring star. The 11-year
cycle of the sun's magnetic field accounts for many of the cool features
of the sun: sunspots, solar flares, and aurora borealis. At the beginning
of the cycle, the magnetic field is weak and there are very few sunspots;
later, at the peak of the cycle, the magnetic field is strong, and there
are many sunspots. Sunspots are relatively cool areas that appear as dark
patches on the face of the sun. They occur where magnetic field lines are
twisted below the surface. The period of time when the magnetic field is
strong and there are many sunspots is called a solar maximum. The sun is
approaching one of its solar maximums right now in the year 2000, and this
maximum will affect conditions on earth.
For example, the aurora borealis, or "Northern Lights" we see in the sky
are much brighter during a solar maximum. They are also more spread out over
the sky. In normal years the northern lights can only be seen
over the poles,
but during a solar maximum they are visible to much of the northern United
States and Europe. Aurora borealis is caused by the solar wind that blows
off the corona of the sun. The temperature of the corona is so high that
the gravity of the sun cannot hold on to it, so hot charged particles from
the corona regularly fly off the sun at millions of miles per hour. When
these particles collide with atoms in the earth's atmosphere, they excite
their electrons, causing them to "jump" to a higher energy level. When electrons
jump to a higher energy level they release photons which are the particles
of light. All of these released photons cause the atmosphere to glow, and
we see the northern lights. Well, when the sun is at solar maximum, the speed
and density of the solar wind goes up, and there are many more northern lights.
Another example of the way the sun interacts with the earth is solar flares.
Remember that sunspots occur when magnetic field lines are twisted below
the surface of the sun, well, solar flares occur when magnetic field lines
are twisted above the surface of the sun. Solar flares are huge explosions
on the surface of the sun that occur near sunspots. They can release as much
energy as a billion megatons of TNT.
You might think
that this huge a burst of energy has got to effect the earth somehow, and
it does. Big solar flares send so much electrical energy to earth that they
have been known to blow out huge portions of the power grid, disable
million-dollar satellites, and even corrode metal pipelines. During a solar
maximum there are many more solar flares than normal. Because of this threat,
we have launched the SOHO satellite into space to sit between the sun and
the earth and monitor the sun's activity. It can give us some advanced warning
if a solar flare is headed our way.
A third example of how the sunspot cycle effects the earth is more interesting, but also more controversial. Scientists have found that the 11-year solar cycle isn't the same every time. The sun goes through this cycle like a pendulum, but the pendulum is an unstable one. Sometimes the pendulum can "overshoot" and throw things out of whack, causing there to be long periods where solar maximums are very violent, or are very calm. The most well known example of this is the "Maunder Minimum," which occurred from 1645 to 1715. It was a 50 year where period there are almost no sunspots at all, even during solar maximum. This period is called "the quiet sun." The interesting thing is, during this Maunder Minimum, the average temperature of the earth went down, glaciers advanced, and we had a "little ice age." New England had summertime frosts, the Thames River froze abruptly in London, and there was no aurora borealis in the sky at all. The pendulum can also swing the other way, such as during the 11th and 12th centuries, when we had a long period of an overly active sun. And, interestingly, during this period, the average temperature of the earth went up. Much of the northern cool areas thawed, which was probably was a factor in the Vikings being able to find and inhabit Greenland.
The Maunder Minimum and other periods like it were verified by looking at
tree rings. A radioactive isotope of carbon, Carbon 14, is formed in the
earth's atmosphere when it is struck by cosmic rays from the sun. When the
sun's magnetic field is strong (during a solar maximum), less cosmic rays
strike the earth, and when it is weak (during a solar minimum), many cosmic
rays strike the earth. Trees record in their rings how much carbon 14 is
in the atmosphere, and during the Maunder Minimum
tree rings had
very high levels of Carbon 14.
Thus, there seems to be a link between the sunspot cycle and the climate of the earth, with solar minimum bringing cooler temperatures and solar maximum bringing warmer ones. This, plus the beautiful displays of northern lights, and the threatening danger of solar flares, are just three ways we are effected by the solar cycle of the sun.
References for information and pictures
Solar Physics. Hathaway, David H. NASA. March 17, 2000.
Sunspots as Predictors. Younce, Matthew Wiley.
The Sun-Earth Connection. NASA/GSFC. USB/S
Introducing the Aurora. Terry, Kathee and Anderson, Hugh. July 12, 1999.
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