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Nov. 8, 2016 | A half-century ago, a team of scientists from the National Center for Atmospheric Research (NCAR) trekked to a point 13,000 feet above sea level in a remote region of Bolivia. There they set up a massive new camera, designed and built by expedition leader Gordon Newkirk and team member Lee Lacey, and waited for a total solar eclipse to cast a shadow on the arid plateau.
Once the moon and Sun aligned, Newkirk and Lacey pulled the trigger on their new device — a combination of telescope, camera, and innovative filter — and hoped for the best. They wouldn't know it until the film was developed, but on Nov. 12, 1966, the scientists had captured perhaps the finest picture of the solar corona ever taken up to that time.
Astronomer Jack Eddy, a former student of Newkirk's, described the importance of the image in a 1988 publication of the International Astronomical Union: "[The] picture was worth a thousand words, and more, for it revealed associations that had never before been seen; oft reprinted, it guided a fresh understanding of the solar corona as the product of magnetic forces and the outward flow of the solar wind. It made the field lines that hold the corona together at once visible throughout the coronal form, giving to coronal physics what x-rays had once given to medicine."
By the time researchers from NCAR's High Altitude Observatory (HAO) arrived in Bolivia in 1966, people had already been photographing solar eclipses for more than a century. But even the best picture could only reveal a portion of the solar corona. The problem was that the brightness of the solar corona drops off drastically as the corona extends away from the Sun's surface into space. So a photograph that was correctly exposed to capture the corona at the Sun's edge could not pick up any details of the outer corona.
Newkirk's innovation was to create a radially graded filter, which blocked more light at the Sun's surface and increasingly less light toward the outer reaches of the corona. In effect, he balanced the brightness, allowing the entire structure of the corona to be captured using a single exposure. A major challenge, however, was that with no opportunity for a second chance, the exposure needed to be estimated correctly the first time so that the narrow band of brightness would reveal the details of the coronal structure.
"At just the right instant, [Newkirk] had to start the automatic programmer, which carried out a pre-determined sequence of exposures, with and without filters… , in the somewhat less than two minutes of totality afforded at the Bolivian location," read an article in the Fall-Winter 66/67 edition of the NCAR Quarterly. "Newkirk's greatest achievement, in the eyes of his colleagues, was that he did choose the correct exposure."
The Newkirk White Light Coronal Camera, still on display in the lobby of the NCAR Mesa Lab in Boulder, became the workhorse of HAO eclipse expeditions in the decades that followed. The camera was used for eclipses in Mexico (1970), Kenya (1973), India (1980), Siberia (1981), Java (1983), the Philippines (1988), Hawaii (1991), and Chile (1994).
HAO scientist Alice Lecinski worked with the camera on the eclipse expeditions in Hawaii and Chile. She said the camera endured the test of time because it was both simple and extremely useful.
"It's a very special camera and dear to my heart," Lecinski said. "For every eclipse, it worked like a champion. The thing that didn't always work was the weather."
The telescopic camera was built on aluminum tripods that could be easily adjusted, and it didn't require a huge power source, unlike modern coronal cameras, so it could more easily be taken to remote locations.
"Its tripod structure is very clever," Lecinski said. "By making the legs longer or shorter, the camera can adapt to any latitude and any hour of the day that the eclipse occurs. It's a simple design and very elegant."
By 1994, HAO scientists were also using a digital camera along with the Newkirk White Light Coronal Camera. Four years later, when HAO scientists traveled to Curacao to observe the eclipse, the Newkirk camera stayed home.
The 1998 eclipse expedition ended up being HAO's last — until 2017. Next year, when a total solar eclipse will cut across the United States on Aug. 21, HAO scientists will again be watching with their instruments.
Researchers Philip Judge and Paul Bryans are working on a project to measure the infrared light emitted by the corona, a property that has never been thoroughly surveyed before. The hope is to better understand how the Sun's magnetic field may be responsible for heating up the corona, which, puzzlingly, is millions of degrees hotter than the Sun's surface.
The effort will include measuring infrared radiation from the ground and the air using instruments mounted in a trailer that will be driven up to Wyoming and onboard the NSF/NCAR Gulfstream V research aircraft.
The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.