EARTH SCIENCE > SUN-EARTH INTERACTIONS > SOLAR ACTIVITY > CORONA
The outermost, high temperature region of the solar atmosphere. Above the
chromosphere and transition region, consisting of almost fully ionized plasma
contained in closed magnetic field loops, called coronal loops or expanding out
along open magnetic field lines to form the solar wind. The corona is a highly
rarefied, low density gas, with electron densities of less than 10*16
electrons/ m*3, heated to temperatures of millions of degrees. The corona is
visible to the unaided eye as a white halo during a total eclipse of the sun.
The Cambridge Encyclopedia of the Sun, The Cambridge University Press,
Cambridge, CB2, 2RU, UK, 2001.