Saying “sun” conjures up positive images of warmth, light, and growth. Yet like every star, our Sun is a place of great violence, a giant sphere of superheated plasma converting 4 million tons of matter into energy each second. For this week’s cover, we needed a dramatic way of showing both the Sun and one of the occasional brilliant light surges known as a flare. Caused by disturbances in the Sun’s intense magnetic fields, flares are organized into five categories of intensity, with those in the “X” class being the strongest. The paper in this week’s issue of Science presents research on predicting these giant flares, which can present radiation hazards. Flares may also be accompanied by emissions of charged particles called coronal mass ejections. If large enough, such ejections can disrupt power grids and communication systems.
Since the late 1950s, satellites have studied our Sun, seeking to better understand the forces governing its behavior. One key observatory is NASA’s Solar Dynamics Observatory (SDO), which since 2010 has used multiple cameras to produce exceptionally detailed images of the Sun. We focused on showing one of the flares presented in the paper, an “X” class flare taking place in March 2012. We needed to determine which of many images SDO captured of this event best showed both flare and Sun. I worked with multimedia producer Scott Wiessinger and data visualizer Tom Bridgman, both with NASA’s Goddard Space Flight Center.
SDO, Wiessinger explained, captures images in 10 different wavelengths. Some wavelengths don’t show flares brightly. “304 angstroms [a unit for measuring wavelengths of light] is a beautiful wavelength, fantastic for showing eruptions of prominences from the Sun,” Wiessinger said. “But the flares look small. That wavelength doesn’t capture the high-energy photons associated with flares.”
For our cover, we needed something more dramatic, revealing the Sun’s roiling surface, yet capturing details of the flare’s high-energy eruption. We were attracted to the image shown in wavelength 131 angstroms and its surprising teal coloration. “This captures the brightest flare image, with the most detail,” Wiessinger said. But 131 didn’t show the interplay of forces on the Sun’s surface very well. Could we do something better? Wiessinger suggested blending together two different wavelengths. “171 angstroms has beautiful loop structure and very fine detail. It’s one of the prettiest wavelengths,” he said. He blended an image in that wavelength with our first choice of the 131 angstroms image, trying the combination in a variety of colors.
Joining the images from both wavelengths revealed the intricate structures on the Sun’s surface and detailed the brilliant X-class flare. Combined with a warm color palette Wiessinger selected, we had the arresting Sun we needed to brighten the cover of this week’s issue.
Bill Douthitt is the Photography Managing Editor at Science.