Nasa is dispatching a specialised research aircraft to pursue the Moon's shadow as darkness sweeps across the northern hemisphere during today's solar eclipse.
The WB-57 high-altitude jet will fly over Iceland, where totality will be visible at an altitude of 50,000ft, well above the clouds, water vapour and atmospheric turbulence that might otherwise compromise observations.
Its target is the Sun's corona, the outer atmosphere stretching millions of miles into space that ordinarily remains invisible against the overwhelming brightness of the solar surface.
By tracking the eclipse path at 460mph, the aircraft will be able to observe the corona for close to three minutes, compared with just over two minutes available to ground-based watchers.
Concealed within the jet's nose cone is an array of four cameras designed to produce high-resolution imagery of the corona across multiple wavelengths of both visible and infrared light, recording the dynamic behaviour of the Sun's atmosphere.
Among the key scientific objectives is the so-called heating paradox, the unexplained phenomenon whereby the solar atmosphere reaches temperatures millions of degrees above those found at the star's surface.
Researchers also hope to study superheated plasma loops erupting from the Sun and gauge the acceleration of the solar wind.
Kelly Korreck, Nasa's eclipse programme manager in Washington, said: "From our unique perspective on Earth during a total solar eclipse, scientists can study the Sun's corona in a way we can't from anywhere else in the solar system."
She added: "The Sun impacts our daily life, satellites and astronauts in space, and we can take advantage of this moment to advance our understanding of that influence."
Beyond the jet mission, Nasa is also launching scientific balloons from both Iceland and Spain to examine how the abrupt loss of sunlight affects the Earth's boundary layer - the lowest portion of the atmosphere, in direct contact with the ground.
This atmospheric zone normally drives weather patterns, as heat rising from the surface generates turbulence and wind currents.
After sunset, cooler air stabilises the layer, producing the calmer conditions typical of night-time, a process known as the boundary layer's "collapse."
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Scientists want to determine whether an eclipse can replicate this effect.
Matthew Bernards, a chemical engineering professor at the University of Idaho who leads one of the Iceland teams, said: "The planetary boundary naturally settles during the evening, dropping to what's known as a nocturnal boundary layer, and we want to characterise how quickly that changes due to the eclipse.
"Will this eclipse be able to collapse the boundary layer?"
In 1868, French astronomer Pierre Janssen identified what proved to be an entirely new element, helium, while conducting spectroscopy during a total eclipse in India.
British astronomer Norman Lockyer later named it after the Greek word for the Sun.
The 1919 eclipse enabled Arthur Eddington to confirm Einstein's general relativity by photographing stars near the obscured Sun and demonstrating that gravity bends light.
More recently, Italian and Australian researchers discovered that mature trees in the Dolomites transmitted bioelectrical signals to younger spruces before an eclipse, possibly responding to subtle gravitational shifts.
Dr Amir Caspi, principal investigator of Nasa's eclipse mission, said: "The Sun is always changing. Every eclipse is different. So we could see things we didn't see before."
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