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By Root 374 0

speedy rate of about 240 miles a second, or about a million miles an hour (London to Paris in about three quarters of a second), bleeding off 10 million tons of hydrogen and helium from our sun every year—a trivial amount, considering its mass. This solar wind reaches Earth in about two to three days, before passing on through the solar system. It hits us in a spiral shape, mostly because of the sun's own rotation. This spiral has been given the homely moniker "the sprinkler" because it rather resembles the spray pattern of an ordinary lawn sprinkler. The sun's magnetic influence also pushes Earth's own magnetic field into a cylindrical shape, facing away from the sun— the solar wind compresses the sunward side of the magnetosphere downward close to Earth, to within six to ten times the radius of the earth, and conversely drags out the night-side magnetosphere to perhaps one thousand times Earth's radius. This end of the spiral is called the magneto tail.

The sun's magnetic energy doesn't penetrate all the way to the planet's surface, because one magnetic field cannot easily penetrate another. Earth's own magnetism deflects that of the sun, thereby helping to keep us alive. If our planet's core was made of, say, aluminum, we'd all be dead.

Within the magnetosphere are two doughnut-shaped radiation belts, sometimes known as the Van Allen belts after NASA scientist James A. Van Allen, whose Geiger counter on the probe Explorer I discovered them in the 1950s.

The inner belt, which circles Earth above the equator, is populated, in the scientific jargon, by high-energy electrons, mostly caused by cosmic rays, that readily penetrate spacecraft and that can, on prolonged exposure, damage both instruments and the people who use them. This belt is not quite a neat circle; the offset between Earth's true north and magnetic poles causes it to reach downward to about 150 miles above the Atlantic near Brazil, causing the South Atlantic Anomaly, a kind of Bermuda Triangle of near space. Low-orbiting satellites frequently pass through it, and are frequently damaged and sometimes fatally zapped as a consequence.

The outer belt is less hazardous but also less stable, and subject to electronic and magnetic storms. It tends to wax and wane with the sun's eleven-year sunspot cycle.

These Van Allen belts, it seems obvious to the conspiracy buffs who populate the Web's wilder shores, make it perfectly clear that the penetration of space has never happened, that man has never been to the moon, and that the Russian space station is really just a set built in the Nevada desert by Russian Communists and their American stooges. If gamma rays lurk in the belts and can kill astronauts, then obviously you would need tons of lead shielding to survive them, and so just as obviously no one has ever been through them alive—QED.

The facts, as they usually are in these cases, are rather less dramatic. It's true that both manned and unmanned spacecraft tend to stay out of the Van Allen belts if they can, but it is equally true that traveling at speed through the belts would yield a radiation exposure of about i rem (at 25 rem you start to show symptoms; at 100 you are dead). The principal hazard in the belt is not cancer-inducing gamma or X-rays, which readily penetrate most substances, as Superman could have told you, but high-energy electrons and protons, which are not difficult to shield against. In addition, the belts span only about 40 degrees of Earth's latitude, 20 each side of the equator, and so if the path of a spacecraft were inclined 30 degrees to Earth's equator, it would bypass all but the edges of the belts.

So, as with the ionosphere, why should we care? Astronauts need to care, but do we? How do the radiation belts affect the air, and therefore the winds, and therefore the climate, if at all?

We know that magnetic storms have caused current surges in power lines, causing blackouts. They also cause static interference that interrupts radio and television signals and cause dead zones for cell phones, to the annoyance of teenagers everywhere.