Hi pendleton,
What a fascinating question. The sun has been shining for about 4.5
billion years, and has enough hydrogen fuel to "burn" for about 10
billion years! Sunspots are dark areas of irregular shapes on the
surface of the Sun. Their short and long-term cyclical nature has been
established in the past century. Galileo discovered sunspots in 1613,
and in 1859 Heinrich Schwabe announced the discovery of the sunspot
cycle.
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SunSpots
Sunspots Exporatorium/Segway/Sun-Earth Connection
http://www.exploratorium.edu/sunspots/
--- Browse through the various subjects provided at the top of the page -
Introduction, History, Modern Research, Activity, Glossary ---
(Most of the Subjects listed have several pages of information...
click on the 'next' button.)
"Dark spots, some as large as 50,000 miles in diameter, move across
the surface of the sun, contracting and expanding as they go. These
strange and powerful phenomena are known as sunspots.
[edit]
"According to George Fischer, a solar astronomer at the University of
California, "A sunspot is a dark part of the sun's surface that is
cooler than the surrounding area. It turns out it is cooler because of
a strong magnetic field there that inhibits the transport of heat via
convective motion in the sun. The magnetic field is formed below the
sun's surface, and extends out into the sun's corona.
[edit]
"While it's easy to understand gas pressure (as gas is heated it
expands, increasing pressure, and as it cools, it contracts,
decreasing pressure), magnetic pressure may be a tougher concept to
grasp. David Dearborn explains, "If you take those places where there
are concentrations of magnetic field and put them together, they have
pressure of their own. You can feel magnetic pressure when you take
two magnets and take the ends of the same polarity and try to put them
together. The just don't quite want to go together. That's magnetic
pressure.
"George Fischer and David Dearborn answer the question, "What is a
sunspot?
Think of a sunspot as a bubble of magnetic pressure, surrounded, by
the gas pressure of the photosphere. For the sunspot to exist, the
total pressure must be in balance between the region inside and the
region outside of the sunspot. David Dearborn elaborates on how
magnetic fields keep sunspots cooler: "Outside a sunspot, you have
only gas pressure, which depends on the temperature. In the sunspot
you have both gas pressure and magnetic field pressure combined."
Since the pressure must be in balance, magnetic pressure inside the
sunspot allows the gas pressure (and thus the temperature) to remain
lower than the areas outside of the sunspot.
[edit]
"Sunspots are made up of two parts: a dark, roughly circular central
disk called the umbra, and a lighter outer area called the penumbra.
The term "umbra" means "shade" in Latin, "penumbra" means "almost
shade." The granular appearance of the area outside of the sunspot is
the result of convection. The center of each granule is hot material
rising from the sun's interior, while the edges are cooler material
sinking downward.
[edit]
"In the last few decades, the forces behind sunspots are becoming
better understood, but we've known for over a 150 years that sunspots
appear in cycles. The average number of visible sunspots varies over
time, increasing and decreasing on a regular cycle of between 9.5 to
11 years, on average about 10.8 years. An amateur astronomer, Heinrich
Schwabe, was the first to note this cycle, in 1843. The part of the
cycle with low sunspot activity is referred to as "solar minimum"
while the portion of the cycle with high activity is known as "solar
maximum.
By studying the sun's magnetic field, modern astronomers have
discovered that the cycle covers twenty-two years, with an eleven-year
cycle of sunspots above the equator followed by an equal cycle below
the equator. According to Fischer, "the overall magnetic field
structure changes in a way that is very interesting: It turns out that
the magnetic fields primarily point from west to east in the Northern
Hemisphere (of the sun), and from west to east in the Southern
Hemisphere. In the next eleven-year cycle, the fields are reversed. So
the cycle is really twenty-two years.
[edit]
"Scientists today have discovered a lot about the way the sunspots
affect the earth. According to Dearborn, "The sunspot itself, the dark
region on the sun, doesn't by itself affect the earth. However, it is
produced by a magnetic field, and that magnetic field doesn't just
stop, it comes to the surface and expands out above the surface...."
Hot material called plasma near a sunspot interacts with magnetic
fields, and the plasma can burst up and out from the sun, in what is
called a solar flare. Energetic particles, x-rays and magnetic fields
from these solar flares bombard the earth in what are called
geomagnetic storms. When these storms reach earth, they affect us in
many ways.
[edit]
"These energetic electromagnetic bombardments can also disrupt power
grids and radio transmissions on earth. Both the flow of electric
current in wires and the transmission of radio waves through the air
can be interfered with by the energetic magnetic radiation from the
sun. Often, these storms produce surges in the power grid and static
on the radio, and if the waves of energetic particles are strong
enough, power grids can be overloaded, and radio signals drowned out.
As Dearborn says, "The particles from the sun that get a little deeper
into the earth's magnetic field can get trapped in the field and
oscillate back and forth between the poles, which produces the aurora
that we can see and enjoy. But at the same time, they produce a lot of
radio interference, which at the lower radio frequencies can be so
loud that you have difficulty broadcasting.
Since satellites are outside of the protection of the earth's
atmosphere, they are particularly vulnerable to the severe geomagnetic
storms that can result from sunspot activity.
*****
Physlink.com
http://www.physlink.com/Education/AskExperts/ae250.cfm
"Sun spot activity rises to a maximum on an 11-year cycle, and this
year will be one such peak.
The main cause of sun spots relates to the rotation of the Sun, and to
its magnetic fields. Because the Sun isn't a solid object but mostly
made up of compressed gases and plasma, different regions rotate at
different speeds. Since the Sun's magnetic field is partially embedded
in this unevenly moving material, it becomes gradually distorted and
twisted. At those locations on the Sun where this distortion is most
pronounced, the fields are strongest. At these points sun spots are
most likely to occur.
*****
How Stuff Works
http://www.howstuffworks.com/sun4.htm
"It is not known what causes this 11-year cycle, but two hypotheses
have been proposed:
Uneven rotation of the sun distorts and twists magnetic field lines in
the interior. The twisted field lines break through the surface
forming sunspot pairs. Eventually, the field lines break apart and
sunspot activity decreases. The cycle starts again.
Huge tubes of gas circle the sun's interior at high latitudes and
begin to move toward the equator. When they roll against each other,
they form spots. When they reach the equator, they break up and
sunspots decline.
*****
You can read more about our sun at the HowStuffWorks website. How the
Sun
written by Craig C. Freudenrich, Ph.D.
http://www.howstuffworks.com/sun4.htm
*****
You can see a map of the far side of the sun at: Helioseismic
Mapping the Far Side of the Sun
http://www.sunspotcycle.com/glossary/farside.html
"The false colors represent condensations of magnetic flux -- that is,
sunspots. This holographic map captured April 12, 2001, shows the
giant sunspot AR9393 on the back side of the Sun a full week before it
emerged into direct view over the Sun's eastern limb. MDI holographic
images reveal the Earth-facing side of the Sun 70 degrees from the
disk center, and the far side of the Sun 50 degrees from disk center.
*****
Sunspots in History
http://www.spaceweather.com/java/sunspot.html
31 Jul 2003 Today's sunspot number is 63
Courtesy National Oceanic and Atmospheric Administration
Updated: 30 Jul 2003
Approximately 1/4th down on the page is a Sunspot Plotter
"Were you born during a solar maximum or minimum? Did the Great
Depression occur during a dearth of sunspots? Was WWII waged under an
active sun? Find out here. Using the pull-down menus below enter your
birth date, or any other date that interests you, and hit "Refresh".
(I was born during a solar minimum.)
*****
Picture of sunspot with ordinary white light
http://zebu.uoregon.edu/~soper/Sun/sunspots.html
Here is a picture showing the details of a sunspot group
http://zebu.uoregon.edu/~soper/ImSun/sunspot.gif
Measuring Magnetic fields on the Sun
http://zebu.uoregon.edu/~soper/Sun/magnetograms.html
*****
Google Search: sun spots, sunspots, cause of sunspots, sunspot cycles
Best regards,
tlspiegel |
