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Spectrograph, Prime Focus


Display Status:

This object is on display in the Explore the Universe exhibition at the National Air and Space Museum in Washington, DC.

Collection Item Summary:

This spectrograph and camera assembly were built to be used at the prime focus of the Caltech 200-inch Hale Telescope at Palomar. It was designed primarily to photograph the spectra of faint extragalactic objects at the very limits of detection. To do so, it has interchangable cameras made to be as photographically "fast" or efficient as possible, working at focal ratios of 1.0 and 0.5. Called either the prime focus spectrograph or the nebular spectrograph fopr the 200-inch telescope, it was designed by Rudolph Minkowski and built at the California Institute of Technology in the late 1940s. In 1951 the prisms were replaced by a diffraction grating and the instrument remained in use continually from 1951 through 1973, providing a wealth of data on the redshift 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 is the main body of the instrument, consisting of the entrance slit, folding mirrors, a collimating mirror, a slot for various gratings, and an aperture for interchangable cameras.

This instrument assembly was donated to NASM by the California Institute of Technology in 1998. It is now on display in the Explore the Universe gallery. In the accesison process, the Museum conducted video interviews with two astronomers who had intimate knowledge of the device.

Collection Item Long Description:

Data Source

National Air and Space Museum


Do not reproduce without permission from the Smithsonian Institution, National Air and Space Museum

Credit Line

Gift of the California Institute of Technology Palomar Observatory. No restrictions.


Overall - cast and welded iron, glass, mixed metals


3-D: 45.5 × 21 × 25cm (17 15/16 × 8 1/4 × 9 13/16 in.)

Country of Origin

United States of America



Inventory Number