Spectrograph, Prime focus, Plate Holders, Photographic

Boxed set of photographic plate holders from the the prime focus spectrograph of the 200-inch Hale Telescope at Palomar operated by the California Institute of Technology. These plate holders carry small glass photographic emulsions. They would be inserted one by one into one of the two fast solid Schmidt cameras of the Prime Focus Spectrograph. The plates were designed to clip into a four-vaned spider that lightly pressed the plate directly onto a field flattener and assured alignment. The overall system was designed by Rudolph Minkowski and built at the California Institute of Technology in the late 1940s. The instrument remained in use continually from 1951 through 1973, providing a wealth of data on the redshifts of distant galaxies, on white dwarf stars, and on the nature of radio galaxies, found to be optically stellar and hence called quasi-stellar radio sources, or quasars.

This instrument assembly was donated to NASM by the California Institute of Technology in 1998. In the accession process, the Museum conducted video interviews with two astronomers who had intimate knowledge of the device.

This instrument was designed primarily to determine the shift of spectra of distant extragalactic objects towards longer wavelengths. This so-called redshift provides a measure of the rate at which objects are receding from the earth and thus the rate of expansion of the Universe. Data obtained with this instrument was used to refine the Hubble Constant that is derived from those measurements. It was donated to NASM by the California Institute of Technology in 1998.