A feature in the low chromosphere of the Sun; also spelt fibril. Fibrilles are fine dark lines arranged in a near-spiral pattern around sunspots as seen in Hα light. They are particularly prominent around large, mature spots, from which they extend outwards for about 10 000 km, forming a superpenumbra. The whole pattern lasts as long as the active region containing the sunspots, but individual fibrilles live for only 20 min or so. Fibrilles are thought to delineate the magnetic field in the chromosphere around sunspots.
Subjects: Astronomy and Astrophysics.