Scientists from several research institutes will aim new detectors at the sun's corona during the February 26 solar eclipse, searching for structures they've never before observed. The researchers are funded in part by the National Science Foundation (NSF), and are from several research institutes, including the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. The scientists will use NSF's C-130 Hercules aircraft to conduct many of their studies.
This eclipse, which takes place in totality over the Caribbean, promises to be one of the most heavily studied in recent history. The data scientists gather could lead to better prediction of the coronal mass ejections that launch solar storms -- the magnetic disturbances that play havoc with communications and electric power grids here on earth. The expedition to be conducted in late February has been inspired by new theories and new technology, the researchers say.
The corona, or outer atmosphere of the sun, is a million times dimmer than the solar disk itself. Scientists can observe the corona at any time using a coronagraph -- an instrument that blacks out the disk -- but sunlight scattered by earth's atmosphere masks the very faint coronal light. A "real" eclipse gives much better results, because the moon blocks sunlight before it reaches the earth's atmosphere and is scattered.
Solar physicists can't send instruments too close to their subject because its heat would melt their probes. In spite of that, however, the structure of the magnetic fields of the corona has been theorized since the late 1800s. These fields, while weak, are sufficiently strong that they underlie and organize everything that happens in the corona.
"Nobody has actually measured the strength of the magnetic field under average coronal conditions, because it's so weak," explains NCAR solar physicist Philip Judge. Because of the faint signal, exacting observations must be made with minimal interference from the earth's atmosphere. Detection instruments mounted on the C-130 aircraft will enable scientists to make the needed measurements, as the aircraft can fly above most of the absorption introduced by water vapor into the earth's atmosphere.
Detection of the magnetic field's signal could build the case for constructing a measuring device called a coronal magnetograph. The kinds of questions that could then be addressed include the nature of the evolution of coronal fields during the solar cycle, and what launches solar flares and the coronal mass ejections that cause disrupting "space weather." The late February effort is a first step, maintains Judge. "We won't really know what's going on in the corona, until we can measure the magnetic field."
A new infrared camera will also make its debut on the C-130. The camera's infrared array detector was recently declassified for peacetime use. It will be used to detect interplanetary dust particles, invisible to sensors so far. The glare of the sun normally obscures such infrared emissions, so an eclipse is a rare opportunity to look for this dust with new technology.