On the morning of April 17, 1967 radio astronomers used the 26-m Telescope at the Dominion Radio Astrophysical Observatory (DRAO) in British Columbia and the 46-m Telescope at Algonquin Radio Observatory (ARO), 3074 km away in Ontario, to make the first successful transcontinental radio astronomical observations using Very-Long Baseline Interferometry (VLBI). This technique allows signals from widely separated telescopes to be combined and effectively form a single telescope, in this case 3074 km across.

Interferometry over short baselines had been practised since the 1940s, using telescopes connected in real time by cable or radio links over distances up to about 200 km. Discussions of the feasibility of VLBI began in 1960, and investigations into technical challenges in how to provide accurate and stable timing and recording of signals at widely separated locations followed in Canada and elsewhere. The DRAO 26 m Telescope had been operated since 1959 and, with the completion of the ARO 46-m Telescope in 1966, the stage was set for making VLBI observations in Canada, with observations of the quasars 3C273 and 3C245 made successfully at 448MHz in 1967.

DRAO 26-metre telescope

From these beginnings, VLBI has become an indispensable tool not only for radio astronomy, but also for geodesy, allowing precision surveying over large distances to millimetre accuracy. The significance of VLBI was quickly recognized, and in 1971 the American Academy of Arts and Sciences awarded the prestigious Rumford Prize to the members of three pioneering VLBI research groups, including the team from Canada that made the historic first observations.

Canadians have continued to be innovators in the field of VLBI, with plans for a continent-wide array of radio telescopes in the 1980s. Although never built, it served as inspiration for the Very Long Baseline Array (VLBA), which was completed in the USA in 1993 and has operated successfully ever since.

Canada was also heavily involved in the first Space-VLBI mission, the Japanese-led VLBI Space Observatory Platform (VSOP), which saw a radio telescope launched into Earth orbit and operated successfully in a VLBI network with ground-based telescopes from 1997–2003. Canada provided the digital signal processing (DSP) hardware that combined the signals to form images, including the correlator that was designed, built, and housed at DRAO, and was also instrumental in key science programmes conducted with VSOP. The DSP experience gained at DRAO in executing the VSOP project was key in the development of the Canadian WIDAR correlator, the heart of the Expanded Very Large Array (EVLA).

Canada's achievement of conducting the first trans-continental VLBI observation in 1967 has now been recognized by the IEEE Milestones Program, which honours significant technical achievements in Electrical Engineering and Computing, with an emphasis on technological innovation and excellence for the benefit of humanity. A bronze plaque commemorating the achievement was unveiled during a ceremony at the DRAO 26-m Telescope in September 2010.