MWO Michelson Building
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Astronomical interferometry was developed at Mount Wilson Observatory as early as 1919 with the 20-foot Interferometer atop the 100 Inch telescope, and later, the 50-foot Interferometer in this building.
Historical Highlight
(by: Don Nicholson)
The interest aroused by Georgia State University's announcement of
their plan to build the world's largest visible light stellar
interferometer on Mount Wilson reminds us that the mountain is the
site of a number of such pioneering instruments. The first, of
course, was the 20 foot interferometer designed by Michelson and
placed on the 100 inch telescope in 1920. With it, Michelson and
Pease made the first direct measurements of stellar diameters and
confirmed the prediction that some stars were huge beyond
imagination. That instrument, wrapped in canvas, is still stored on
the first floor of the 100 inch dome.
Ten years later Pease completed work on a new, but much larger interferometer. This instrument, with a mirror separation of up to 50 feet, was to be capable of measuring diameters of stars less than one- half the size of those measured on the 100 inch. Too large and heavy to be mounted on the 100 inch, it was housed in its own building just east of the 60 inch. Pease was able to confirm the measurements made with the 20 foot interferometer but the 50 foot never lived up to his expectations. It had state-of-the-art design and construction for its time, but the art of the time was not up to the precision requirements of such an instrument. The optical path lengths from the outer mirrors to the eyepiece must be maintained to just a few wavelengths of light. Thermal gradients within the support beam and its deflections were too great to permit an observer to compensate adequately. Had Pease the foresight to invent the laser and the computer, all would have gone well.
The building that housed the interferometer is still standing and has been converted to office and shop space. The trestle over which the roll off shed moved was largely dismantled to provide space for another stellar interferometer--the infrared instrument of the University of California. This instrument was conceived by and is operated under the guidance of Nobel Laureate Charles Townes--who did contribute to the invention of the laser. This writer has wonderful memories of that fine building and its extensive trestle which was one of the best jungle gyms ever constructed.
My thanks go to MWOA sustaining member Carl Fielding for providing me with a copy of Francis Pease's October 1930 article in the Scientific American. Carl is the proud owner of the 40 inch parabolic mirror which was the primary for the 50 foot interferometer. He is currently incorporating it into a transportable telescope which he hopes someday to bring to Mount Wilson for a trial.
Near the Michelson Building, across from the 60-inch dome, is a small building: the Galley. On the other side of a small hill to the east is another interferometer, the Infrared Spatial Interferometer operated by UCB.
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A Crash Course in Interferometry |
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The 50' Interferometer |
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