The sun and the planets, the moon and the satellites of the other
planets, the comets, asterois, and meteoroids make up the solar system.
The solar system is located in the Milky Way Galaxy. Almost the whole
galaxy is made of stars. Astronomers believe there are at least 100
billion stars. If you counted one star a second it would take you more
than thirty thousand years to count 100 billion. And each star has
planets, like the sun.
The big burning ball of gas that holds nine major planets in orbit is
not unlike many stars in the universe. The Sun makes up 99.86 percent of
the solar system's mass and provides the energy that both sustains and
endangers us. Scientists have lately begun calling its tremendous
outpouring of energy "space weather."
The Sun can be divided into three main layers: a core, a radiative zone,
and a convective zone. The Sun's energy comes from thermonuclear
reactions (converting hydrogen to helium) in the core, where the
temperature is 15 to 25 million degrees. The energy radiates through the
middle layer, then bubbles and boils to the surface in a process called
convection. Charged particles, called the solar wind, stream out at a
million miles an hour.
Magnetic fields within the sun slow down the radiation of heat in some
areas, causing sunspots, which are cool areas and appear as dark
patches. Sunspot activity peaks every 11 years. The next peak is due in
During this so-called solar maximum, the sun will bombard Earth's
atmosphere with extra doses of solar radiation. The last peak, in 1989,
caused power blackouts, knocked satellites out of orbit and disrupted
radio communications. (See our special report on Sunspots.)
Though NASA scientists aren't predicting any record-setting space
weather in 2000, the peak is expected to be above average. "It's like
saying we're going to have a mild or cold winter," says Dr. David
Hathaway at NASA's Marshall Space Flight Center. But as communications
rely increasingly on satellites, there are more targets in the sky and
more significant consequences to any disruptions.
And there may be more to sunspots than disrupted communications. An
active sun, known to heat the Earth's outer atmosphere, may also affect
our climate. Scientists say a small ice age from 1645 to 1715
corresponded to a time of reduced solar activity, and current rises in
temperatures might be related to increased solar activity.
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The Sun frequently spews plumes of energy, essentially bursts of solar
wind. These solar flares contain Gamma rays and X-rays, plus energized
particles (protons and electrons). Energy is equal to a billion megatons
of TNT is released in a matter of minutes. Flare activity picks up as
Effect on Earth
The Sun's charged, high-speed particles push and shape Earth's magnetic
field into a teardrop shape. The magnetic field protects Earth from most
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