Inner Corona

Inner corona — click to enlarge


The bright inner corona during totality on August 21, 2017 was captured with a Canon 40D and Canon 100-400 zoom lens at 400 mm, f/8, 1/250 sec, ISO 100.

The reddish regions are solar prominences, part of the sun’s chromosphere layer. The chromosphere is, of course, always present — some of the chromospheric activity that extends high enough above the surface may become visible at the “edge” as the sun rotates — this is never seen during the day because the photosphere drowns it out (unless one views through a special “hydrogen alpha” filter), but does become visible through binoculars during totality. Whether or not solar prominences are visible during an eclipse is pure luck.

The solar prominences are red because the chromosphere emits light at the “hydrogen alpha” wavelength, 656.28 nm, which is in the red part of the spectrum. “Hydrogen alpha” photons are emitted when a specific electron transition occurs in the hydrogen atom (between the 3rd and 2nd energy levels).