Yesterday, the vernal equinox, the sun returned to the Northern Hemisphere at last. Nothing here or anywhere else in our corner of the galaxy would exist without the sun, yet a surprising number of solar mysteries persist. Much of heliophysics is focused on "space weather," predicting what the sun will do. That's because solar flares and coronal mass ejections spew charged particles and radiation into space, occasionally toward Earth. These seething bursts of energy can jeopardize telecommunications on the ground and in space, not to mention the lives of astronauts.
But there are plenty of other, perhaps more profound, burning questions: how does the star actually work? What's inside it? What, exactly, it is belching out at us?
Check out our gallery of some burning questions about the sun.
Ephraim Fischbach, a physics professor at Purdue University, is trying to figure out whether solar particles are messing with radioactive materials on Earth, for instance. Something is definitely happening; it's just that no one can explain it yet.
New spacecraft like the Solar Dynamics Observatory could help answer some of these questions.
"We're moving toward a weather-type analysis, what has to happen inside the sun to see what will happen outside the sun. If we get a model for that, we need to test it, and that's the data the satellites are giving us," said W. Dean Pesnell, project scientist for the Solar Dynamics Observatory at NASA's Goddard Space Flight Center. "We are asking people to give us a far more detailed analysis of the sun than other stars or planets."
In celebration of the sun's return to the northern hemisphere - and NASA's Solar Week festivities - here we take a look at some major questions scientists still have about the sun, and the ways new spacecraft are helping answer them.
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