title: Emission-line variability and distance of quasars.
abstract: The radius of the line-emitting region in quasars is larger than 1 parsec for the cosmological hypothesis and smaller than 1 parsec for the local hypothesis. Variability in emission lines has been reported but not proved beyond doubt. Its time scale would be a direct observational indicator of this radius and would add an important element to the discussion of the origin of quasars. Objects that are variable in their optical continuum seem to be the most promising ones to look at for line variations, and they should be observed spectroscopically at regular intervals.
authors.forename: J
authors.initials: J
authors.lastname: Pfleiderer
authors.forename: M
authors.initials: M
authors.lastname: Grewing