It might not seem obvious why anyone should care what's happening on the other side of the Sun. But NASA can explain: our home star is a seething, roiling ball of superhot gas that goes through cycles of relative quiet, punctuated by violent outbursts. Every so often, the Sun spits out a blob of charged subatomic particles — and occasionally, one of them is aimed directly at the Earth.
These eruptions, known as coronal mass ejections, aren't enough to hurt the planet physically; they're very hot, but also very insubstantial. What they can do is fry the electronics of communications satellites, and even put astronauts in danger of a radiation overdose.
These electronic storms are part of the broader phenomenon known as "space weather," and it's good to have as much warning as possible when the Sun is looking angry. (See a total eclipse of the sun.)
The problem is that its angry face might be turned away from us, and it takes 12 days or so for the far side to rotate into view. That's one major reason that NASA launched the twin STEREO spacecraft (for Solar TErrestrial RElations Observatory) in 2006 to take up positions orbiting on opposite sides of the Sun.
The satellites constantly image the Sun in several different wavelengths of light, which come from various layers near the Sun's surface, because the sunspots and magnetic storms that generate space weather — just like hurricanes and thunderstorms on Earth — have a three-dimensional structure.
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