solar corona

During a total solar eclipse, the Sun's corona and prominences are visible to the naked eye. The solar corona is the outermost layer of the Sun's atmosphere. It is a region filled with relatively hot, tenuous plasma that is structured by the solar magnetic field.

The solar corona lies above the photosphere and chromosphere and extends out to the edge of the solar atmosphere where it merges with the solar wind. The chromosphere and corona are separated by a thin, highly dynamic transition region. The outer edge of solar atmosphere where the corona transitions into the solar wind is defined by the Alfvén surface which forms an irregularly shaped boundary around the Sun at heights ranging from about 10 to 20 solar radii (7000000 to 14000000 km) above the photosphere.