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Quick Look High-Resolution Structure in the Sun's Corona: A New Frontier for SwRI Involvement in Solar Eclipse Observations, 15-9071 Printer Friendly VersionPrincipal Investigators Inclusive Dates: 02/03/98 - 06/03/98 Background - Historically, total eclipses of the sun have been the cornerstone of observational solar physics, dramatically enhancing the understanding of the solar corona, the wispy, awe-inspiring part of the sun visible from the ground for only a few minutes each year. Recent dramatic improvements in CCD cameras and high-speed computers are greatly improving ground-based eclipse observations, once again providing opportunities for significant advances in understanding the fine scale structure of the solar corona. New high-spatial resolution, white light coronal observations obtained with the Canada-France-Hawaii Telescope (CFHT) on Mauna Kea, Hawaii, during the July 11, 1991 total solar eclipse revealed considerable fine structure in the solar corona up to the resolution limit of roughly one arcsecond (1/3600 degree). The observations revealed relatively bright and dark continuous isolated threads, or narrow tubes, in the coronal cavity (a region with a lower electron density in the corona) near a large prominence (a cloud of material visible above the solar disk). Depending upon the interpretation, the distribution of measured intensities suggest a span of electron density ranging from zero to twice ambient in the finer threads, indicating that the highest contrast isolated dark threads, or tubes, are fully evacuated or hollow! Approach - The overall goal of this project was to perform an enhanced, more controlled, and radiometrically stable form of this important new experiment during the eclipse on February 26, 1998. The most significant improvement in SwRI’s approach was the use of a digital, radiometrically stable, high-speed CCD camera, and high-speed computer instead of photographic film used during the earlier eclipses. Accomplishments - The research team had spectacular success at the eclipse, with the experiment working perfectly and clear skies permitting a time series of more than 120 high-resolution images of the inner solar corona, revealing detailed loop structure and time evolution. Moreover, the team gained valuable experience in performing eclipse observations, working closely with collaborators from the High-Altitude Observatory at the National Center for Atmospheric Research (NCAR). A sample of the observations, shown below, is published on the SwRI Eclipse website at http://www.boulder.swri.edu/~hassler/eclipse98/. Detailed analysis of the time series observations, searching for evidence of Alfven wave propagation in the corona, is ongoing and will be published in the journal Solar Physics. The experience from this successful eclipse expedition has permitted SwRI to secure outside funding from National Science Foundation, the National Geographic Society, NASA Ames Research Center, and the Research Corporation to observe the August 11, 1999 solar eclipse in Europe. Moreover, SwRI obtained high visibility and extensive publicity, with articles in several international newspapers and a news clip shown on the ABC News and the Discovery Channel.
The first image (left) shows the moon beginning to occult or "swallow" the limb of the sun. Second from the left is an image of "Bailey's beads", or bright beads of sunlight along the moon's limb, caused by sunlight shining between the mountains of the moon. Also visible are giant magnetic loops of plasma called prominences. The right two images are sample images of the corona above the southwest limb of the sun during the eclipse (taken one minute apart), showing both open- and closed-loop magnetic structures. These images have been processed with an unsharp masking technique to increase the contrast of subtle features. The field-of-view of these images is 6 x18 arcminutes, with roughly 1.4 arcsecond per pixel spatial resolution. More than 120 images were taken roughly 1.6 seconds apart to form a time series, or movie, to look for changes or wiggling of the small scale structures, which might be a sign of waves traveling along the magnetic field lines and heating the atmosphere. |
