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There
is no doubt that the Sun is immensely important to us here on Earth. Without
it there would be no light and no life. Hanging over us a million times
bigger than the Earth, the Sun dominatesour lives, inspiring our ideas
in fields as diverse as science, art and religion. However,
in cosmic terms, the Sun is a fairly average star. It is middle-aged, medium
sized and has a mediocre surface temperature of 6000ºC. But
it is this middle-of-the-road character that makes the Sun our ideal companion.
If the Sun was a hot blue star, then the Earth would have been fried long
ago. And if the Sun were a cool red giant, then our current location would
place the Earth right inside it. The Sun, like all stars, is a huge atomic
factory, fusing hydrogen atoms together to form helium. Amazingly, the
Sun burns its fuel at the rate of 4 million tonnes per second. But even
at this pace, it will not start running out of supplies for 5 billion years.
Although the Sun looks very uniform to us here on Earth, probes such as
TRACE and SOHO have photographed the Sun directly, showing it to be a seething
mass of chaotic energy. The root of this turbulence is the constant battle
between the Sun's powerful magnetic field and its spinning otion.The
Sun has a magnetic field and a North and South pole, just like the Earth.
But unlike the Earth, the Sun doesn't rotate as a solid body. The
equator revolves faster than the poles and so, as the Sun spins round,
its magnetic field lines wind up like a spring. Eventually they reach
breaking point and burst, resulting in the total reversal of the Sun's
magnetic field. So the poles swap round periodically in a cycle lasting
22 years. This is actually happening to the Sun at this very moment as
it reaches the climax of its current cycle in 2001. This enormous upheaval
is the cause of the Sun's uneven features, such as sunspots and prominences.
Sunspots are regions of strong magnetic force that spread across the Sun
periodically. Prominences are huge sprays, surges or loops of stellar
material that shoot above the surface. These are areas where the churning
magnetic field lines have burst out, dragging layers of burning gas with
them. Sometimes these cause solar flares, releasing particles into space
that can affect man-made satellites around Earth. |
