Is the magnetic field protecting Earth from deadly radiation about to reverse direction or even dissapear?

One of the most daring clandestine operations of World War II was the 1944 sinking of the Norwegian ferry Hydro with its cargo of "heavy water" destined for the Nazis' secret atomic bomb project. Although the mission was declared a success, no one ever established if the special shipment was actually on board. In this program, NOVA descends 1,300 feet beneath a remote Norwegian lake to find the answer.

Everyone has heard of global warming, but a lesser-known man-made phenomenon has been nearly as powerful at affecting Earth's climate. A look at global dimming, created by soot and pollution reflecting the sun's rays and surprisingly helping to offset global warming's catastrophic advance.

It contains 99.9 percent of all the matter in our solar system and sheds hot plasma at nearly a million miles an hour. The temperature at its core is a staggering 27 million degrees Fahrenheit. It convulses, it blazes, it sings. You know it as the sun. Scientists know it as one of the most amazing physics laboratories in the universe. Now, with the help of new spacecraft and Earth-based telescopes, scientists are seeing the sun as they never have before and even recreating what happens at its very center in labs here on Earth. Their work will help us understand aspects of the sun that have puzzled scientists for decades. But more critically, it may help us predict and track solar storms that have the power to zap our power grid, shut down telecommunications, and ground global air travel for days, weeks, or even longer. Such storms have happened before—but never in the modern era of satellite communication. "Secrets of the Sun" reveals a bright new dawn in our understanding of our nearest star—one that might help keep our planet from going dark.

In April, 2010 the eruption of Iceland's Eyjafjallajökull volcano turned much of Europe into an ash-strewn no-fly zone, stranding millions of travelers. But was Eyjafjallajökull just the start? Now, an even more threatening Icelandic volcano, Katla, has begun to swell and grumble. Two more giants, Hekla and Laki, could erupt without warning. Iceland is a ticking time bomb: When it blows, the consequences could be global. As CGI takes us inside these geological monsters, we meet atmospheric scientists who are working to understand just how devastating an eruption could be—not just for air travel but for the global food supply and for Earth's climate.