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Solar system


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."


Massive energy


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.


Solar flares


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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

sunspots increase.


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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