|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 Fisher 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.|
| More About the Sun
To better understand the process
that creates sunspots we first need to learn more about the sun. The sun
is by far the largest object in the solar system, containing more than 99.8%
of the total mass of the solar system (Jupiter contains most of the rest).
The sun is made of about 75% hydrogen and 25% helium by mass, with tiny
trace amounts of metals and other compounds. Over time, the nuclear fusion
reactions that fuel the sun are converting hydrogen into helium in its core,
changing the ratio of the two elements.
The energy produced by nuclear fusion in the
core of the sun is carried outward by convective motions in the outer 20-30%
of the sun, called the convection zone. Convection is the process by which
hot gas from the center of the sun rises to the surface, and cooler gas,
which comes to the surface and radiates its heat away, sinks back towards
The scale of the sun is hard to fathom.
The sun is so large and so dense that it takes about 50,000,000 years for
energy produced at its core to make its way to the sun's surface!
The sun has been radiating light and heat for the past four or five billion
years. The sunspots to which this site is devoted appear as tiny spots on
the sun--but an average-sized sunspot is as large as the earth.
Magnetic Fields and the Solar Dynamo
The sun, like the earth, generates
a magnetic field that permeates the surface and extends out into space.
The sun's magnetic field moves and changes over time, fluctuating in intensity
in different areas of the sun's surface. The sun's magnetic field is thought
to be produced by fluid motions within and just below the convection zone,
something Dearborn refers to as the "solar dynamo," but the ultimate
source of the sun's magnetic field, and the reasons for its fluctuations,
is not well understood.