Seyfert galaxies are about 10% of all galaxies, and are some of the most intensely studied objects in astronomy. They are thought to be powered by the same phenomena as quasars, although they are closer and less luminous than quasars. These galaxies have supermassive black holes at their centers which are surrounded by accretion discs of in-falling material. The accretion discs are believed to be the source of the observed ultraviolet radiation. Ultraviolet emission lines and absorption lines are the best way to analyse the surrounding material.