On the morning of November 12, 1966, nine employees of Livermore Laboratory’s Test Division were aboard a U.S. Air Force C-135 aircraft, some 500 miles off the coast of Argentina. Racing across the South Atlantic at speeds of over 600 miles per hour, their mission was to keep pace with the moon’s shadow as it passed across the sun to view and record the fleeting phenomena associated with a total solar eclipse. For those on the ground, the totality was to last less than two minutes. However, for the airborne scientists racing the moving shadow, an extra precious minute of experiment time was expected to be gained. A precious minute, considering that, in the past century, there had only been 100 minutes of total observation time.
The purpose of the expedition was to perform certain measurements of the sun’s corona, as well as other features, that were possible only when the sun’s brilliance was masked by an eclipse. Among the Livermore-developed equipment and experiments aboard the aircraft was a Fabry Perot interferometer for measuring the widths of several emission lines (thus the temperature) of the solar corona, two spectrographs for analyzing the corona’s composition, and a time-lapse photography experiment designed to analyze the coronal structure. In addition to eclipse data, two other experiments, cosmic ray studies and airglow studies, were to be conducted.
Preparation for the flight had begun more than a year earlier; and, by mid-October 1966, the Livermore-designed and fabricated equipment had arrived at Kirtland Air Force Base in New Mexico, where it was installed on the C-135. On Nov. 6, the Livermore team, led by Test Division’s Robert Donaldson, arrived in Buenos Aires, where they conducted practice flights to ensure that all the equipment was functional. Up till that time, weather had been cloudy, and it was uncertain whether the aircraft could surmount such high overcast conditions.
However, on Nov. 12, 1966, morning dawned clear and bright, and for a total of 3 minutes and 22 seconds of twilight, Livermore camera shutters clicked, capturing a variety of sights and data in an event not to occur again for years.
In June 1973, Livermore scientists once again raced the shadow of the moon during one of the longest solar eclipses in 1,400 years. That June, three Livermore Test Division scientists, Erv Woodward, Jose Cortez and Bob Donaldson, joined a 30-member Solar Eclipse Expedition sponsored by the Atomic Energy Commission (AEC) — today’s Department of Energy — and the National Science Foundation (NSF). Like the 1966 expedition, their mission was to gather spectral data from the sun’s light rings and its chromosphere, the thin layer of plasma between the sun’s visible surface and the corona.
On June 30, the expedition departed from Torrejon Air Force Base in Spain toward the Sahara Desert in north Africa. For 11 minutes and 55 seconds, data was captured as the U.S. Air Force flying laboratory raced the moon’s shadow along the path of the total eclipse. For most of the scientists on the 1973 expedition, glimpses of the eclipse came only in the form of lines on an oscillograph or as lights on a spectrometer, as the view from most of the plane’s windows was completely obscured by scientific equipment. However, Livermore’s Woodward and Cortez considered themselves amongst the lucky, as they actually got to view and photograph the eclipse from their all-important perch in the aircraft’s rear bathroom.
In addition to the main experiments conducted aboard the U.S. Air Force aircraft, other AEC-NSF experiments for the 1973 eclipse were conducted aboard a prototype French Concorde supersonic jet. With top speeds of almost 1,300 mph (Mach 2), the Concorde was able to capture an astounding 74 minutes of data, as it tracked the moon’s shadow, which was travelling at 1,354 miles per hour.