Volume 45 number 2 (2017)
(Abstract only) The author designed and built a slitless spectrograph to record reference marks along the spectrum of a point light source. Spectra can be taken of transient, clustered, or moving lights when a spectrograph cannot be accurately aimed at the lights to capture slit spectra. Three beams of undispersed light, directed by mirrors and lenses, provide reference marks. Near each end of the spectrum a reference mark barely varies from the corresponding point on the spectrum when the aim toward the light source varies. Within 2 degrees of perfect aim toward the light source, the variation is less than 7 angstroms. The third reference mark enables this variation to be quantified. The locations and orientations of the optical components are mathematically derived. Additional features of the spectrograph enable the use of a slit and comparison spectrum, and the recording of higher orders by moving the camera and using specific Wratten filters.