History
The search for radio sources in the sky began when Heinrich Hertz first demonstrated the existence of radio waves in 1888. After decades of non-detection on bright sources such as the Sun, in 1933 Karl Jansky at Bell Labs discovered cosmic radio waves originating from the Milky Way. With the improvement in sensitivity and reliability of radio systems during World War II, the discovery of radio sources other than the Sun and the Milky Way became commonplace, at the time lead by groups at the Universities of Cambridge and Manchester in England, and the Commonwealth Scientific and Industrial Research Organization in Australia.
In the late 1940s, Lee Dubridge (Caltech's president), Robert Bacher (professor of physics and chairman of the Division of Physics, Mathematics, and Astronomy); and Jesse Greenstein (founder of the astronomy department at Caltech), expressed an interest in bringing radio astronomy to the Caltech community. At first this was met with resistance by optical astronomers at Caltech. After much perseverance, they hired John Bolton to design Caltech's first radio telescope, to be built at the newly established Owens Valley Radio Observatory (OVRO).
After John Bolton and Gordon Stanley built a prototype 32-foot telescope at Palomar, it was moved to OVRO in 1958. The main scientific motivation for the radio telescope was to obtain accurate position information on radio sources to better correlate them with the high-resolution optical images obtained with the Palomar observatory. This is best done with an interferometer, and so in the late 1950s construction began on the first interferometer at OVRO. It consisted of two telescope, 90 feet in diameter, arranged on railroad tracks. At its widest separation, the interferometer could achieve positional accuracy of better than a few seconds of arc for bright sources. By observing the same source at a variety of telescope spacings and frequencies, the interferometer also provided information on the structure of the source, as well as its spectra. The interferometer became operational on its East-West arm on Christmas, 1959. A North leg was completed in the following year. At that time, the OVRO telescopes were the most sensitive in existence.
In addition to improving on the location of various radio sources, OVRO telescopes were used extensively to study hydrogen clouds in the Milky Way. In the early 1960s the fully operational interferometer was used to make images of sources, and found that most extragalactic radio sources are double, consisting of two well-separated clumps of radio emission. Closer to home, though, the OVRO interferometer was used to determine an offset in Jupiter's magnetic and rotation axis.
In the 1960s, improvements to the detectors on the OVRO interferometer allowed it to make the best images of the radio sky the world had yet seen. With the dishes on movable tracks, and the improvement of its surface, the OVRO interferometer was able to image sources at wavelengths as small as 1 cm.
By studying regions rich in hydrogen gas throughout our galaxy, the telescopes at OVRO were integral in determining that spiral galaxies do not contain most of their mass towards their centers. In fact, the speed of these gas clouds around galactic centers is nearly constant the further you go out. These flat rotation curves are strong evidence for dark matter being a basic constituent of the universe.
In the 1970s OVRO's two-dish interferometer was overtaken by larger and faster telescopes in Holland and England. In 1979, it was then converted to studying solar physics, and it has since been mapping the sun daily over the 1 to 18GHz frequency range.
In the early 1960s the National Science Foundation funded a prototype 40-meter telescope to be built at the Owens Valley. This telescope was to be one of eight in an array, arranged over roughly 5 miles of tracks in the Owens Valley. Unfortunately, by the end of the 1960s the plans to build the interferometer were ended with the construction of what is now known as the Very Large Array (VLA) in New Mexico, but at that point OVRO did have a 40-meter prototype telescope in operation.
After its dedication in 1968, the 40-meter telescope was used in conjunction with the existing interferometers, forming a baseline of roughly 3/4 of a mile. Another use of the 40-meter starting in 1969 was as a station in the Very Long Baseline Interferometer (VLBI). In this capacity the signal from 40-meter telescope was combined with that of the Parkes telescope in Australia to form the longest baseline achieved at that date, capable of resolutions of 0.4 thousands of a second of arc. Studies with the OVRO-Parkes baseline confirmed the existence of quasars as extremely small and extremely energetic objects. The 40-m continued to operate as a VLBI station until late 1991 when the Very Long Baseline Array (VLBA), run by the National Radio Astronomy Observatory, came on line.
In the 1980s, the main focus at the observatory was on the construction of an array of 10.6 meter (34-foot) telescopes to pick up millimeter-wavelength radio signals. The antennas, designed by Caltech professor Bob Leighton, remain to this day some of the highest surface accuracy radio telescopes ever made. The array consisted of three antennas when it was dedicated in 1985. Three more dishes were constructed on site, the last being dedicated in 1996. The interferometer of six 10-meter dishes operating at 1mm and 3mm wavelengths was one of the most powerful millimeter arrays in the world. It was used to make many important discoveries about star-forming regions, protostellar disks, protoplanetary disks and galactic structure. Even though the hot summertime air at OVRO feels dry, the moisture content is so high that millimeter observations are nearly impossible. In 2005, these telescopes became part of the Combined Array for Research in Millimeter-wave Astronomy (CARMA). Located 3,000 feet higher than OVRO near Westgard Pass, the low water vapor content made it possible to make observations year-round. Due to lack of funding, the array was shut down in 2015 and the telescopes were moved back to OVRO. We have plans for the telescopes and the 'Research' link at the top of the page will take you to a page describing our current research projects.
For more on the history of OVRO you can read the articles by Professor Marshall Cohen which he wrote for Caltech's Engineering and Science magazine, which cover the history of the observatory.
The Owens Valley Radio Observatory: The Early Years (1994)