Gaertner measuring machine

Exposing a plate at the telescope was only the start. To be useful, the data it held had to be extracted and reduced. Extraction meant measuring features on the plate to turn them into numbers; reduction entailed adjusting those numbers until they contained only real physical information about the source. Only then, in their extracted and reduced form, could the data be properly interpreted and their import understood.

The instrument above was made by the Gaertner Scientific Corporation of Chicago and acquired by Lick around 1900. It is a microscope with an adjustable stage, for extracting data from spectrographic plates. A plate placed on the stage could be moved slowly and precisely as the astronomer examined it through the eyepiece. When a spectral feature of interest appeared in the microscope, its position relative to other features or to a calibration spectrum, also on the plate, could be read from the graduated scales at left.

Lick Historical Collections, catalog no. SO000420