A small, very bright point in solar active regions, visible in filtergrams tuned to the line wings of the Ηα‎ line. Ellerman bombs occur at the footpoints of arch filaments, often in the early stages of the development of major active regions. An alternative name is moustache, from the appearance of the Ηα‎ line, which has emission wings extending either side of a dark core. It is named after the American astronomer Ferdinand Ellerman (1869–1940).