An Etymological Dictionary of Astronomy and Astrophysics

An area in the → solar corona which appears dark in X-rays and ultraviolet light. The gas density in these
areas are very low, about 100 times less than that of coronal → active regions. The magnetic field lines in a coronal hole extend out into → interplanetary space rather than returning to the Sun’s surface, as they do in other parts of the Sun (→ open magnetic field line). Ionized hot gas can escape easily along such a path, and this brings about
high speed → solar wind streams.

See also: → coronal; → hole.