Here Comes the Sun

Since even before the dawn of civilization, the sun has been essential in farming, religion, and telling time. It's a star that's been worshipped and studied, and so to celebrate our 30th anniversary, correspondent Martha Teichner looks at the history of the sun, as well as a look forward to the future.

What exactly is the sun?

"It's a big ball of hydrogen gas," said Owen Gingerich, professor of astronomy and history of science emeritus, at the Harvard Smithsonian Center for Astrophysics.

Not so big. In fact, kind of middling for a star … but enormous compared to the Earth.

"It's one thing to say, well, the diameter of the sun is 100 times the diameter of the Earth," Gingerich told Teichner. "But you don't really get the impression of how big the sun really is unless you can see it in three dimensions."

How old is the sun? "About five billion years," said Gingerich, who assured us, "it's just about halfway through its lifetime."

It's really hot, maybe 28 million degrees Fahrenheit at its core, and it's burning up. There are nuclear reactions going on inside it all the time. When the energy works its way to the surface, we see it as sunshine..

At the relatively safe distance of 93 million miles away, the Earth orbits around the sun. It takes 365 days … a year. Life-giving time for planting and growing and harvesting crops.

No wonder so many civilizations built great monuments, like Stonehenge in England, to plot the seasonal doings of the sun, or Chichen Itza in Mexico, or the Konark Sun Temple in India.

No wonder the sun was a god to the ancient Egyptians, the Greeks, the Romans, the Incas.

They knew then that the sun influenced almost every aspect of their existence. We know now it even determined the color of our skin.

"Our ancestors who evolved close to the equator have very darkly pigmented skin, adapted to very high levels of radiation," said Nina Jablonski, head of the anthropology department at Penn State University and an expert on skin.

"And then as we dispersed away from the equator, in our evolution we evolved lightly pigmented skin to cope with less solar radiation," Jablonski said.

Around the equator the earliest humans developed a kind of permanent suntan. This dark coloring containing something called melanin. How's this for amazing: Melanin acted like a natural sunscreen, blocking ultraviolet radiation but allowing in exactly the right amount of vitamin D.

"We need vitamin D," Jablonski said. "So the sun shines, ultraviolet B shines on the skin and makes vitamin D chemically in the skin, right there."

Now fast forward to, say, present-day Scandinavia, where sometime around ten thousand years ago people lost their permanent tans. In northern weather, under a weaker sun, they don't require protective color.

Speaking of weather … there is actually solar weather, and we're all affected by it.

Richard Fisher heads NASA's heliophysics division, which studies solar activity. He showed us images from 2003 when there was lots of sunspot activity.

"These guys are pretty big!" he said. "They're as big as Jupiter, 40,000 kilometers across."

Sunspots are intense magnetic fields, and when a lot of them appear, it's a signal that a season of violent solar weather is on the way.

The sun flings out swirling streams of electrical current called solar winds, and when they reach the Earth's atmosphere, we see the spectacular aurora borealis, the northern lights.

NASA can also simulate solar storms, in order to see these great explosions of radiation and magnetic particles erupting from the sun's atmosphere, called its corona.

"We'll see one of these disturbances on the sun, understand its direction, and we just start the stopwatch and say, 'Well, it's gonna be about, you know, fifty hours and we should expect to see a possible solar-induced effect at the Earth," said Fisher.

And that means trouble. An astronaut on a space walk could actually die from exposure to the radiation. Communications systems on planes flying over the poles often fail. GPS signals get screwed up. In 1989 a solar storm incinerated a transformer in Quebec, leaving 6 million Canadians without power...

For NASA, learning how to predict solar weather so that disruptions can be planned for (or even prevented) is a practical justification for the seventeen satellites it has in space already analyzing the sun, with more to come.

In a NASA "clean room," Fisher showed us the next satellite to go into orbit, the most sophisticated solar observatory that's ever been in orbit. "It is the cornerstone of our NASA program for about the next decade," he said.

Its planned launch, November. Its mission, barely thinkable even ten years ago ... in effect, a sonogram of the sun's gassy interior.

Yes, deep inside, where solar weather forms. It should send back pictures ten times better than high definition television.

But can those images beat our view of the sun, with the horizon as its stage, and the power to move us ...

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