Westerhout came to the US in 1962 as Professor and Director of Astronomy at the University of Maryland where, during the next 15 years, he grew a 12 graduate student department into one of the nation’s prominent astronomy programs. In 1972, Dr. Westerhout organized the University of Maryland's division of mathematical, physical and engineering sciences and was named its head the next year. He continued his research with a 21-cm survey that used the 300-foot radio telescope of the National Radio Astronomy Observatory to extend to higher angular resolution our knowledge of Galactic structure. He often flew a rented plane between Maryland and Green Bank with his programmer, Heinz Wendtland. He continued at Maryland in that role through 1973, with additional responsibilities from 1972-73 as Chairman of the Division of Mathematical & Physical Sciences and Engineering. He was a Visiting Astronomer at the Max-Planck-Institut für Radioastronomie in Bonn, Germany in 1973-74.
In 1977 he left the University of Maryland to become the Scientific Director of the U.S. Naval Observatory in Washington DC. While there, he guided the evolution of that observatory toward astronomical data obtained from telescopes at the Flagstaff station. He initiated the radio astrometry in 1979 by using the Green Bank interferometer to improve the absolute positions of celestial objects by a factor of ten over the optical. It yielded measurements of the Earth orientation parameter UT1 that were a factor of four better than the PZTs. In the 1980s, he converted to VLBI, again increasing the precision by a factor of ten. He then looked into the use of optical long base line astrometry for absolute positions. This now achieves about an order of magnitude precision over other ground-based measurements but is not as precise as space-based measurements. In the 1980s, he introduced the use of CCDs at Flagstaff’s parallax program that supplanted the use of optical plates, improving the precision by a factor of five. He was responsible for a major expansion of the organization and construction of a network of five radio telescopes from Florida to Hawaii that measured the rotation of the Earth. Westerhout retired in 1993.
Gart Westerhout was an amiable and affable man, a great and noble man, with an exceptional sense of humor and an infectious laugh. He wore a bow tie, had flamboyance seldom found among his academic colleagues, and was held in exceptional high regard by his students. In his early career he smoked cigars, a signature identification. He, Judith and the children became American citizens in 1969. They loved to entertain, and their friendships went far beyond his profession. He was an avid O-gauge model railroader and maintained a detailed layout that took up most of the basement space in his home. Westerhout’s own recollections of his career are included in several hours of oral interviews conducted by Steven Dick at the end of his USNO career and they are deposited at the USNO library. He was a communicant of St. Thomas Aquinas Roman Catholic Church in Hampden.
Westerhout was a member of numerous astronomical organizations, including the Dutch Astronomical Society, International Astronomical Union (Commissions 33, 34, 40, 24 & 5), the American Astronomical Society (Councilor 1975-78 & Vice President 1985-87), the Royal Astronomical Society, the Astronomical Society of the Pacific, the USNC-URSI - Commission J, and Sigma Xi. He contributed his scientific and management expertise widely, for example to the IAU, the National Science Foundation, the AAS, the National Research Council, Associated Universities Inc., the Inter-Union Committee for the Allocation of Frequencies , URSI, the US National Radio Astronomy Observatory, MPIfR, MIT's Haystack Observatory, the Arecibo Observatory, and the National Academy of Sciences.
Westerhout’s awards and special recognition included a NATO Fellowship, a CSIRO (Australia) Fellowship, an Award for the Teaching of Science, Washington Academy of Sciences, Humboldt Prize.
Westerhout was the author of more than 70 scientific papers, reviews and reports. In recognition of his life's work, Minor Planet 5105, discovered by Edward L.G. Bowell, was renamed Minor Planet Westerhout in 1991.
Gart Westerhout died of congestive heart failure on October 14, 2012 at the age of 85 in his home at the Charlestown Retirement Community.