Earth-sized telescope found its roots in Canada: Bob McDonald

Canadian innovation helped pave the way for a project that will photograph a black hole's event horizon for the first time.

Synchronized use of telescopes in Ontario & B.C. were subject of an NFB documentary in 1969

The Event Horizon Telescope, an array of 8 radio telescopes scattered across the globe, are using a technique that was pioneered in Canada in 1967. (NASA)

The Event Horizon Telescope, an array of eight radio telescopes scattered across the globe hoping to image the black hole at the centre of our galaxy, are using a technique that was pioneered in Canada in 1967. And we were first because of perfect timing.

In astronomy, size matters. The bigger the telescope, the better the image and the farther into the universe it can see. But there comes a limit, where mirrors — or in the case of radio telescopes, giant metal dishes — can only get so big before they become unmanageable and begin distorting out of shape from their own weight. So another way to make our eyes in the sky wider is to take two or more telescopes spaced far apart so they act as one big dish the size of the distance between them.

The technique is called interferometry, and it has been in use on smaller scales since the 1950s. A critical part of this technique is timing — that is, both telescopes have to be looking at the same object in the sky at exactly the same time so their signals can be synchronized.  A radio signal from space will arrive at one telescope slightly ahead of the other, and the farther apart the telescopes are, the greater that delay will be.

When the two slightly different signals are combined, an interference pattern appears called fringes, that contain the information about the object in space.

This illustration shows a glowing stream of material from a star as it is being devoured by a supermassive black hole in a tidal disruption flare. (NASA/JPL-Caltech)

Telescopes that are relatively close together can be simply connected by cables and synched with an atomic clock. But Canadian astronomers wanted to make an interferometer the size of a continent, by taking advantage of the fact that during our Centennial Year, Canada had two large radio telescopes spaced 3,074 km apart: one in Algonquin Provincial Park, Ont., the other near Penticton, B.C. Both are still operating today.

Rather than trying to hook these two telescopes together by cable over such a long distance, the scientists used large format tape recorders (which were borrowed from CBC TV because of budget restraints at the time) to record the signals from each telescope, with the idea of bringing the tapes together and playing them back simultaneously.

The 46m antenna at Algonquin Radio Observatory in Algonquin Provincial Park, Ont. (Algonquin Radio Observatory)
But again, the big issue was timing. There had to be an extremely precise timing signal, accurate to millionths of a second on each tape, so they could be synchronized exactly.

To provide that signal, two extremely accurate atomic clocks, were synched together using the National Research Council's atomic clock in Ottawa. One of them was then driven to the Algonquin observatory, only 200 km away, while the other was flown to B.C.

With everything set, both telescopes were pointed at the same time toward a distant quasar, which are among the brightest and most distant galaxies known. The tapes recorded the signals, but when the B.C. tape and its clock were flown back to Algonquin and the two tapes were played back simultaneously, the interferometer effect the scientists were looking for was not there. The task of creating a super telescope was more difficult than it seemed.

One of the big problems was again, timing, keeping the Rubidium atomic clocks in sync with each other. These clocks didn't like to travel. They are usually kept in climate-controlled environments and are sensitive to temperature changes. According to Dr. Joseph Fletcher, one of the pioneers who worked on the project, the clocks would either turn off by accident, or drift away from each other. The tape machines did not run at exactly the same speed because they were designed for television, not astronomy.

Markarian 231, a binary black hole found in the centre of the nearest quasar host galaxy to Earth, is seen in a NASA illustration. (NASA/Reuters)

Power outages were common, which wreaked havoc with the equipment, much of it running on vacuum tubes. They even had to compensate for the fact that the telescopes were sitting on a turning Earth, which constantly changed the timing of the signal between them.

After almost a year of effort, taking into account all of the effects distance and time were having on their equipment, and only a matter of days before a competing American team, they finally got the signal they were looking for, creating the world's first very long baseline interferometer

You can watch this drama unfold as it happened in the National Film Board documentary, To the Edge of the Universe.

Thanks to this Canadian effort, the technique is now used all over the world, and if all goes well, will give us the first ever image of the gigantic black hole that lurks at the very core of our Milky Way Galaxy.


  • An earlier version of this story said the the Algonquin Radio Observatory was no longer in operation. The story has been corrected to reflect that it is still operational.
    Apr 18, 2017 11:02 AM ET


Bob McDonald is the host of CBC Radio's award-winning weekly science program, Quirks & Quarks. He is also a science commentator for CBC News Network and CBC-TV's The National. He has received 12 honorary degrees and is an Officer of the Order of Canada.