The Children's Encyclopedia
Of course, we can't actually see inside
the Sun. No real spacecraft has ever gone there, for it would be melted on approach
by the tremendous heat. How, then, are we able to learn so much about our neighborhood
One way is by breaking the "secret code" contained in sunlight. Amazingly enough,
even the tiniest sunbeam carries with it a great deal of information about the
place in the Sun where it came from.
Secrets of the Spectrum
If we pass sunlight through a glass triangle – a prism – we find that
the light is made, not just of one color, but of many. What looks like white sunlight
is really a mixture of all the colors of the rainbow. The split-up sunlight forms
a spectrum of colors stretching from red through orange, yellow, green, blue,
indigo, to violet.
Using a special instrument, called a spectroscope, scientists can get a much clearer
look at the spectrum of sunlight. In this way they can uncover something even
more surprising about it. Not only is the Sun's spectrum made of many colors,
but it is also crossed by hundreds and hundreds of dark, narrow lines. These are
called Fraunhofer lines in honor of one of the first scientists who noticed them.
The Fraunhofer lines carry the secret code in sunlight. They are made by substances
high up in the Sun that absorb light coming from deeper down. By studying these
lines, scientists have learned what the outside of the Sun is made of and how
hot and dense it is.
The Sun Seen from Earth
Another way we can learn about the Sun is simply by looking at it. The problem
is how to do this safely. If we gazed straight at the Sun or tried to view it
through an ordinary telescope, it would be so bright that it would blind us.
To view the Sun safely, scientists use special solar telescopes These have mirrors
that track the Sun across the sky, collect its light, and form an image, or picture,
of its brilliant disk on a large, flat viewing table.
The bright surface of the Sun is known as the photosphere. It is a bubbling, boiling,
bursting brew of hot gas. Seen through a solar telescope, the Sun's surface is
always shifting, always alive with movement.
There are, for instance, tiny freckles that cover the entire surface of the Sun.
Scientists call these granules and believe they are caused by hot gases that well
up from deeper in the Sun, cool, and then fall back down again. The pattern of
granules presents a dotlike, ever-changing picture.
Sunspots are much larger and darker spots on the face of the Sun. They may last
a week or more and may be big enough to swallow several Earths. A sunspot is an
area of the Sun's surface that has been made a little cooler than its surroundings.
Because the center of the sunspot is cooler than the rest of the Sun's surface,
it looks dark. But a sunspot is still quite hot – around 7,000°F (4,000°C)
– and, by itself, a large one would look as bright as the full Moon!
Sunspots are formed when the Sun's magnetic field bursts up through the photosphere.
Since the magnetic field then usually loops back around into the surface, a second
sunspot may be formed. These loops are the reason sunspots often occur in pairs.
Sometimes there may be no sunspots for several weeks. At other times the Sun's
face seems peppered with them. Their position changes daily as the Sun slowly
turns on its axis. Over a period of years, the average number of sunspots gradually
goes up, hits a peak, and then gradually falls off again. The sunspot peaks happen
about every eleven years, and the whole pattern of their change is known as the
The Sun eclipsed
The bright surface of the Sun that we see isn't where the Sun ends and outer space
begins. The Sun also has a huge atmosphere – a layer of gases outside the
photosphere – that we can't usually see.
Only at a very special time can we get a good view of the Sun's much dimmer atmosphere.
It is during a total eclipse of the Sun.
You may have noticed that the Moon and the Sun seem to be about the size in the
sky. (In fact, the Moon is really much smaller and closer to us.) Once in a while,
the Moon passes exactly between the Sun and the Earth. Then, from some parts of
the Earth, the Sun's bright disk is completely blotted out by the Moon.
During a few minutes of total eclipse, we get a thrilling glimpse of what is going
on above the surface of the Sun. For a short time, just at the start and at the
end of the total eclipse, we see a thin, pinkish, curved ring around the edge
of the Sun. This is the chromosphere - the bottom part of the Sun's atmosphere.
The chromosphere is like a bubbling foam of gases, a few thousand miles deep,
thrown up by the "sea" of the photosphere.
During the middle of the eclipse, we see the beautiful, glowing corona –
the top part of the Sun's atmosphere. Although the corona is made of only very
thin, very hot gases, it is huge. It stretches more than a million miles out from
the Sun in every direction!
Total eclipses also provide us with marvelous views of prominences. These are
great clouds of slightly thicker gas that form in the corona and then rain down
onto the Sun's surface. They look like giant flaming tongues.
Another, rarer type of prominence – the eruptive prominence – is caused
by gas bursting out of the Sun's surface. In fact, it is just one of the ways
in which the Sun can shoot matter into space.
From Sun to Earth
A strange kind of wind – the solar wind – carries about one million
tons of the Sun into space every second! Some of the tiny, fast-moving particles
in the solar wind reach Earth and get trapped in the magnetic field that stretches
all the way around our planet. A small portion of the solar wind particles manage
to leak out at the poles. They rise into the air and cause a wonderful shimmering
glow in the sky. This is how aurorae are made.
The solar wind blows especially hard following a solar flare – an explosion
of the Sun's surface that sends a sudden burst of particles into space. Solar
flares cause magnetic storms around the Earth. For a while, the aurorae become
brighter, and radios and compasses behave in an odd way.
Scientists know of other things, too, that the Sun gives off. Radio waves and
X-rays reach the Earth from the Sun's surface. And huge armies of strange, ghostly
particles, called neutrinos, march out to meet us from the Sun's core.
By building special instruments on Earth, and by launching others on satellites,
we can study what the "radio Sun," the "X-ray Sun," and even the "neutrino
Sun" look like. In this way, we can gain a better understanding of how our neighborhood