Stardate 10:5:97
The focus of our articles the last few
weeks has been our parent star, the Sun. This week, we will look
more closely at our life giving star. Sunspots were first discovered
by Galileo, ending the myth that the Sun was perfect, and without
blemish or marking. Sunspots are cool, magnetically active areas
of the Sun, which form in two eleven year cycles, making it appear
that sunspots appear, migrate, and disappear over an eleven year
cycle, when, in fact, one complete sunspot cycle runs for twenty
two years. The sunspots produced during the second eleven year
cycle have the opposite polarity of the ones formed during the
first half of the cycle. To astronomers studying the Sun in visible
wavelengths, however, sunspots seem to follow an eleven year pattern.
This was first noticed by Heinrich Schwabe in the year 1843. He
was an amateur astronomer working in Germany at the time. The
time when the greatest number of sunspots are apparent (regardless
of their polarity) is known as the sunspot maximum, or solar max.
Conversely, the time when sunspots are at their minimum is known
as sunspot minimum, or solar min. The most recent sunspot maximum
was reached in 1990, and we will see the next solar max in the
year 2001. We are currently in a time near sunspot minimum. Sunspots
are formed by fact that any fluid body, including the Sun, rotates
faster at the equator than it does at the poles. While the equator
of the Sun rotates about every 25 days, it takes the areas near
the poles up to 35 days to complete the same journey. We are all
familiar with the patterns of magnetic force which we found as
children, putting a magnet under a piece of paper, and dropping
iron fillings on it. The Sun, too, has magnetic lines of force
running vertically from pole to pole. If we imagine just one of
these lines of force running from one solar pole to another, we
can easily see how this happens. Now, with your one magnetic line,
imagine what will happen when the equator rotates faster than
the poles. The line becomes stretched more and more, even being
able to make it all the way around to it's starting point before
breaking. What happens when a magnetic line of the Sun breaks?
Well, we can once again use the bar magnet analogy. Each magnet
has a north magnetic pole, and a southern magnetic pole. If we
were to break a magnet in half, we would be left not with a magnet
with only one pole (there's no such thing), but two magnets, each
with a northern and southern magnetic pole. The same thing occurs
when we break magnetic field lines. The two broken ends have different
magnetic polarities. Thus, sunspots are always found in pairs,
each pair with opposite polarities. They form near the equator
of the Sun, slowly migrate to the poles, and disappear. Sunspots
cool the area around them, and a region of sunspot activity may
be only 2/3 the temperature at the surface of the Sun. Flares,
on the other hand, erupt from the surface of the Sun (the photosphere)
with a force of up to 2 billion megatons (the same explosive power
as a billion of the worlds most powerful nuclear weapons going
off at one time), climb high above the solar surface, and crash
back down again with tremendous force. They are composed of ionized
gas, erupting from areas where the magnetic field of the Sun has
been disturbed. Therefore, they are nearly always found above
areas of sunspot activity. A good size group of sunspots can produce
over 100 flares per day! The hot, ionized gas can rise up to 500,000
km (312,500 miles) above the photosphere before crashing back
down again. Solar flares can disrupt communications here on Earth,
but are also the bringers of one of nature's greatest shows, the
aurora borealis, or northern lights.
Clear skies, and good viewing.
