July 22, 2012
Art And Science Collide in New Solar Imaging Technique
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redOrbit Staff & Wire Reports - Your Universe Online
Nicholeen Viall of the NASA Goddard Space Flight Center in Greenbelt, Maryland innovated this new method, which uses various hues splashed across a yellow background to share information about the 12-hour heat history of the sun, the US space agency announced this week.
Each pixel of her images contain "a wealth of information" about the heat history, which NASA said "holds clues to the mechanisms that drive the temperature and movements of the sun's atmosphere, or corona."
"We don't understand why the corona is so hot," said Viall, who described the technique itself, as well as her conclusions about the corona, in a paper published in The Astrophysical Journal. "The corona is 1,000 times hotter than the sun's surface, when we would expect it to get cooler as the atmosphere gets further away from the hot sun, the same way the air gets cooler further away from a fire."
While scientists agree that the roiling magnetic fields of the sun have to transfer energy and heat upwards into the atmosphere, there is still much debate over exactly how that process occurs, the US space agency said. Some say that coronal heating is uniform over a period of time, while others argue that it originates from a number of nanoflares present on the sun's surface. Viall developed her technique in order to resolve the issue.
To start with, she used high resolution images provided by the Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA), which are capable of capturing shots of the sun in 10 different wavelengths, each roughly corresponding to a single temperature of material. By looking at the sun in different wavelengths, she was able to determine how the materials change temperature over time.
Ordinarily, scientists study these types of temperature changes by focusing on the arc-shaped magnetic flux that leap upwards from the sun's surface. They gather information about those arcs by comparing nearly-simultaneous images of the sun in different wavelengths -- a time consuming process that is limited in its focus, and one that is also subject an individual's judgment and/or bias, NASA explained.
"Viall wanted to look at as much of the solar material in a given area of the corona as she could, incorporating information about a variety of temperatures simultaneously," the organization said. "She also wanted to avoid the subjective process of subtracting out the background. Instead, she decided to look at all light coming from a given spot on the sun at the same time. That meant coming up with a visualization technique to convey all that information at once -- and thus her Van Gogh-like images were born."
"For an interesting spot on the sun, Viall examines six channels over an entire 12-hour stretch. She compares each channel to the other channels in turn, assigning it a red, orange, or yellow color if the area has cooled, and assigning it a blue or green color if the area has heated up. She assigns the exact shade of the color based on how much time it took for the temperature change to occur," NASA added.
Viall said that her process essentially measures the time lag that it takes a specific locale to either heat up or cool down. It is completely automated, eliminating the possible human bias in the study of solar areas to study and which to ignore, and all of the material studied and every wavelength is represented statistically, she added.
"Viall's images show a wealth of reds, oranges, and yellow, meaning that over a 12-hour period the material appear to be cooling," NASA said. "Obviously there must have been heating in the process as well, since the corona isn't on a one-way temperature slide down to zero degrees."
"Any kind of steady heating throughout the corona would have shown up in Viall's images, so she concludes that the heating must be quick and impulsive -- so fast that it doesn't show up in her images," they added. "This lends credence to those theories that say numerous nanobursts of energy help heat the corona."