The Sun's Sizzling Corona

"It was a complete and total success," reported Pasachoff when the eclipse was over. "We viewed the two and a half minutes of totality in a completely clear sky. We played back data from our hard drives, and we can see that we have fabulous scientific data. It should keep my students and me busy for years."

Pasachoff's group was not alone. Scientists from many countries captured high resolution images of the corona during totality in search of microflares, magnetic vibrations and other phenomena. High-caliber data obtained during the eclipse may help scientists evaluate another possible mechanism for coronal heating: electrical dissipation.

It's been known since the days of Faraday and Maxwell that if you wave a magnet back and forth in the vicinity of a conducting wire, a current is induced in the wire. The same thing takes place in the sun's atmosphere. Oscillating magnetic fields generate currents that flow through the highly ionised gases above the photosphere and in the corona. How does that heat the corona? When current flows through a resistor some of the energy is dissipated as heat. A common light bulb is a good analogy. Electricity moves through a partially conducting filament, the filament glows and it also become very hot. Again, the question hinges on better observations of magnetic fields and plasmas in the corona. Scientists know that there is some resistive dissipation of energy in the corona, but they can't be sure how much.

There is no shortage of ideas about what may heat the corona. Microflares, magnetic and acoustic waves, and electrical dissipation are all good candidates, but the observed energy flux into the corona from each of these mechanisms is about an order of magnitude too low to account for coronal heating. More and better data are needed to finally reveal the culprit.

"My bet is that it's going to be some mixture," says Hathaway, "but only time will tell! When we do know, we'll have solved one of the big mysteries in astrophysics."