An Etymological Dictionary of Astronomy and Astrophysics

An arc-like structure in the Sun’s → corona that is found around → sunspots and in → active regions. These structures are associated with the closed magnetic field lines that
connect magnetic regions on the solar surface. The loops are sometimes as high as 10,000 km with their two ends situated in photosphere regions of opposite magnetic polarity. This implies that the coronal loops are tubes of magnetic flux filled with hot plasma. They last for days or weeks but most change quite rapidly.

See also: → coronal; → loop.