Secret Worlds of Summer The Sun

Mysteries of Light

By Michael E. Ruane
Washington Post Staff Writer
Tuesday, June 19, 2007

Summer. Such an uncomplicated season. Winter's menace and spring's frenzy are over.

With calmer spirits, we emerge into the sunlight, relaxed enough to ponder mysteries of the universe.

This year's Metro summer series begins -- with the sun, of course.

It is a commonplace, fairly average, class-G star -- not as hot as the O- or B-class stars such as 10 Lacertra or Rigel, nor as cold as the class-M supergiant Antares.

But this star can affect the navigation of homing pigeons and the precision of oil drillers. Its mystery induced the ancients to cut out human hearts in sacrifice. And its light makes the daily 93 million-mile trip to Earth in about eight minutes.

Scientists across Washington are trying to simulate it, harness it and scrutinize it. Beachgoers bathe in it. By August -- or maybe this afternoon -- we'll be cursing it. And at 1:06 p.m. Thursday, its orientation in the sky officially begins summer.

It is our sun -- a giant seething irritable ball of nuclear fusion whose total energy output is so huge that a second's worth of it could meet U.S. power needs for 9 million years.

In religion, it is borne across the sky by the Navajo god Tsohanoai. It was Helios to the Greeks, riding his fiery chariot from dawn to dusk. And in the Bible, it was stopped in its tracks while Joshua slew the Amorites.

It rotates once every 25 days, regularly belching chunks of its insides into space or flinging out fountains of plasma called magnetic loops. It has an 11-year cycle, in which its storm activity ranges from what is called "solar minimum" to "solar maximum."

And it is the capricious source of space weather -- whose forecasting grows more vital as our technology grows more vulnerable.

With a core temperature of 27 million degrees Fahrenheit, the sun can warm and burn, cure and kill, nurture and destroy. One day a few eons from now, scientists believe it will expand and boil the Earth.

Until then, says NASA Goddard Space Flight Center astrophysicist W. Dean Pesnell, it's a great chance to analyze, and use, an actual star up close.

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