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solar minimum

Solar Myth

May 5, 2005: There's a myth about the sun. Teachers teach it. Astronomers repeat it. NASA mission planners are mindful of it.

Every 11 years solar activity surges. Sunspots pepper the sun; they explode; massive clouds of gas known as "CMEs" hurtle through the solar system. Earth gets hit with X-rays and protons and knots of magnetism. This is called solar maximum.

There's nothing mythical about "Solar Max." During the most recent episode in 2000 and 2001, sky watchers saw auroras as far south as Mexico and Florida; astronomers marveled at the huge sunspots; satellite operators and power companies struggled with outages.

Now the sun is approaching the opposite extreme of its activity cycle, solar minimum, due in 2006. We can relax because, around solar minimum, the sun is quiet. Right?

"That's the myth," says solar physicist David Hathaway of the NASA Marshall Space Flight Center. The truth is, solar activity never stops, "not even during solar minimum."

To show that this is so, Hathaway counted the number of X-class solar flares each month during the last three solar cycles, a period spanning 1970 to the present. X-flares are the most powerful kind of solar explosions; they're associated with bright auroras and intense radiation storms. "There was at least one X-flare during each of the last three solar minima," says Hathaway.

This means astronauts traveling through the solar system, far from the protection of Earth's atmosphere and magnetic field, can't drop their guard—ever.

Recent events bear this out: Rewind to January 10, 2005. It's four years since solar maximum and the sun is almost blank--only two tiny sunspots are visible from Earth. The sun is quiet.

The next day, with stunning rapidity, everything changes. On January 11th, a new 'spot appears. At first no more than a speck, it quickly blossoms into a giant almost as big as the planet Jupiter. "It happened so quickly," recalls Hathaway. "People were asking me if they should be alarmed."

Between January 15th and 20th, the sunspot unleashed two X-class solar flares, sparked auroras as far south as Arizona in the United States, and peppered the Moon with high-energy protons. Lunar astronauts caught outdoors, had there been any, would've likely gotten sick.

So much for the quiet sun.

....

Will the sun be quiet when it's supposed to be? Don't count on it.

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