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.
Sunspots
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 2000.
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
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 of the harmful solar radiation, but
extreme flares can disable satellites and disrupt communication signals. The
charged particles also excite oxygen and nitrogen in the atmosphere to create
the aurora borealis, or northern lights. More solar radiation during the
upcoming solar maximum means an increase in the aurora.
Coronal mass
ejections
Similar to a solar flare, a coronal
mass ejection is a bubble of gas and charged particles ejected over several
hours. It can occur with or without solar flares, and can also threaten Earth's
atmosphere.
Final fact
If you stood on the Sun, its gravity
would make you feel 38 times more heavy than you do on Earth. But it's kind of
hot, so please don't try it.
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