Halley's comet photographed from New Zealand in October 1986. The Moon is behind cloud at bottom right. Named after Edmund Halley (1656-1742), who first recognised its periodicity, the comet has been recorded every 76 years since 240 BC. It consists of a nucleus of ice & dust, shaped like an elongated potato. Its tail is formed as the comet is heated when it approaches the Sun. Dust & gas are released and swept into a tail both by radiation pressure and by the solar wind.