Science
The corona, in a few minutes of night
A total solar eclipse is a laboratory. The Moon occults the photosphere so completely that the faint outer atmosphere of the Sun — and the region where the solar wind begins — can be measured from the ground.
Our observations combine high-resolution white-light imaging of the corona with narrow-band filters centred on forbidden emission lines of highly ionized iron, including Fe XI and Fe XIV. Those lines retain the diagnostic power of extreme-ultraviolet spectroscopy, but they can be recorded at much larger heights during the darkness of totality.
From those data we construct maps of electron temperature, ion charge state, and magnetic topology in the acceleration region of the solar wind — a zone that remains difficult to observe any other way. Occasional coronal mass ejections caught in the field of view become experiments of their own.
Why is the corona so hot?
The photosphere is about 5,800 K. A few thousand kilometres above it, the corona exceeds a million. Totality lets us see how that heat is distributed with height and how it relates to magnetic structure.
Where does the solar wind originate?
The continuous outflow that fills the heliosphere is launched in the inner corona. Emission lines of heavy ions mark the freeze-in of charge states and the rise of outflow speed.
What holds magnetic structures in place?
Streamers, prominences, and the large-scale field of the corona evolve over the solar cycle. Eclipse imaging records their geometry at a resolution and inner height that coronagraphs cannot match.