The Galaxy Hα Fabry-Perot System for WHT (GHaFaS) is an astronomical instrument installed on the 4.2 metre William Herschel Telescope (WHT) at Roque de los Muchachos Observatory on the Canary island of La Palma. First light was on 6 July 2007. Its name is a play on the acronym: G alaxy Hα Fa bry-Perot S ystem and the Spanish word " gafas " meaning spectacles. It produces maps, in intensity and velocity, of extended objects in the sky (which could be external galaxies, star forming regions in the Galaxy, planetary nebulae, or supernova remnants, as examples), which radiate in the H-alpha line, emitted by ionized hydrogen in interstellar space. It can also be used for a variety of other lines.