An area on the Sun where strong magnetic fields emerge through the photosphere into the chromosphere and corona above. Active regions on the photosphere include sunspots and faculae; their counterparts in the chromosphere are plages. Other active regions found in the chromosphere are dark fibrilles and filaments. Active regions in the corona are composed of numerous coronal loops in which hot gas flows along magnetic field lines; they are sometimes known as coronal condensations. Flares originate in active regions. Active regions are allocated numbers by the US government’s National Oceanic and Atmospheric Administration (NOAA) in order of appearance. The present numbering system started on 1972 January 5. Four-digit numbers are assigned up to 9999, after which the numbering returns to 0000, as happened on 2002 June 14; the numbers are prefixed by AR for Active Region. Active regions that exist for more than one solar rotation are given a new number each time they reappear.