It was Aug. 14, 2017, just one week before the Moon would cross paths with the Sun and Earth, casting its shadow across the United States. The entire country buzzed with anticipation for the fleeting chance to see the corona, the Sun’s tenuous outer atmosphere, during #Eclipse2017. But the wait was uniquely nerve-wracking for a group of scientists at Predictive Science Inc., a private research company in San Diego: They had just published a prediction of what the corona would look like on Aug. 21, the day of the total solar eclipse. How would their prediction — the result of a complex numerical model and tens of hours of computing — compare to the real thing? After the eclipse, the group found their prediction bore a striking resemblance to the Aug. 21, 2017, corona, although the model lacks many finer structures. This visualization shows the Sun’s three-dimensional magnetic field during one full solar rotation. The Predictive Science researchers modeled magnetic field lines in order...