A fibril is a fine dark line seen in H-alpha light in the low chromosphere of the Sun. Fibrils form whirls near strong sunspots and plages or in filament channels. They connect spots and plages of opposite polarities, running along magnetic field lines, and surround large, mature spots in a radial pattern. Individually, they are about 10,000 kilometers long and last for 10 to 20 minutes.