The sun seems to be a quiet neighbor of light and heat, toasting sunbathers and helping plants rise from the soil. But our nearest star is really a complicated ball of fiery gas, winking with strange sunspots, booming like a giant drum and whipping up wicked storms on its 11,000°F surface.
This weather can cause big problems back on Earth, more than 90 million miles away from the sun's activity. Solar storms can turn compass needles topsy-turvy. They can even knock out electric and telephone service. They've caused satellites to slip out of orbit. Astronauts are also threatened by the solar radiation.
Now scientists are getting a good look at what goes on beneath the sun's blinding halo. Someday they may be able to forecast hot solar storms as accurately as weathermen predict rain and snow on Earth.
Eyes On The Sun
Since December 1995, the Solar and Heliospheric Observatory (SOHO), a spacecraft packed with telescopes, has been circling the sun, snapping photos and measuring waves on the surface.
Last month scientists announced SOHO's surprising discoveries. Among the finds: rivers of superhot gas (plasma) beneath the surface at the sun's poles flow faster than nearby gases.
These polar streams, explains scientist Jesper Schou, are like the jet streams of air high above Earth's atmosphere that influence our changing weather. Such a discovery, he says, "is completely unexpected." SOHO also found twisting bands of plasma that dive deep into the sun's interior and flow back toward the equator. These "trade winds" are like Earth's great ocean currents.
All this may help explain the 11-year solar cycle, which affects sunspots (cooler patches on the surface) and bursts of gas called solar flares. Perhaps, say scientists, this cycle--and the effect it has on Earth--is governed by the flow of various winds and streams beneath the sun's surface.
A network of solar stations around the world has added to SOHO's views of the sun's secret life. Says network director John Leibacher: "I never had any hope that we would be able to see these things."
Other Earth-bound instruments have recorded sound waves that ripple across the sun's surface as gases explode. "It's a terrible din," says scientist Douglas Gough.
Soon even more of the solar environment will be revealed to scientists. On August 25, NASA launched the Advanced Composition Explorer (ACE) to join SOHO in tracking the solar wind. A gush of hot particles (2 million degrees F) that stretches beyond Pluto, the solar wind affects weather on all nine planets in our solar system.
By understanding what lies beyond the sun's blaze, scientists hope to forecast solar weather and predict its powerful effects on Earth. "We used to think the inside of the sun was fairly simple," says astronomer John Harvey. "But that was before we had the capability to see into it."