The sun has always loomed large, bringing heat and light and life. In ancient times, it was worshipped as a god; now we revere it as our local blob of luminescent hot plasma — a close-up example of the twinkling stars that come out at night. The sun shines thanks to fusion reactions deep in its core, melding hydrogen atoms into helium and releasing photons in the process. That light then spends tens or hundreds of thousands of years bouncing around before it finally escapes the sun’s surface.
Life on Earth depends on sunshine — but that dependability belies our star’s complexity. The sun’s outermost visible layer, for instance, is roiled by invisible magnetic fields, which break and reconnect over and over, releasing energy every time. And no one knows why its atmosphere-like corona becomes hotter, not cooler, as you move away from the solar surface.
Learning about the sun is something of a Pandora’s box, says NASA heliophysicist Nicola Fox. “We’ll answer these first questions, but we’ll probably answer them with 10 more questions.”
