John Bolton and Bruce Slee found the center of the galaxy on their lunch hour.

In 1951, these two radio engineers were working for a converted Australian military radar installation, studying radio emissions from the sun. An array of radar dishes picked up radio waves that were bouncing off the ocean. The work was apparently rather boring, so Bolton and Slee hatched a scheme to design a more powerful and precise telescope that they could use for studying celestial radio sources from farther away.

In particular they were interested in finding the center of our Milky Way galaxy. The general area around which the galaxy rotates had been known to astronomers for some time, but it is shrouded in cosmic dust and nobody had ever pinpointed it or seen what it looked like. The relevant part of the sky passes over Australia, and radio waves could penetrate the dust, so it stood to reason that if somebody built a large enough radio telescope there, he could solve the mystery.

Bolton and Slee thought that this sounded like a worthwhile challenge, but they had already been chewed out once for aiming their telescopes at things they weren't supposed to, and they figured that their work array wasn't big enough to get the job done anyway.

Therefore they decided to build their own, and to build it really large.

When most people think of radio telescopes, they picture the mammoth dishes in Socorro, New Mexico, stretching across the desert, gyrating on massive bases to point at common targets. Clearly, Bolton and Slee could not build anything like that in their free time.

However, they could build a disk that pointed at a fixed part of the sky. That wouldn't require nearly as much complexity. And they did not have to build a base for it at all -- this seems particularly brilliant to me -- instead they could dig a dish-shaped pit in the ground, line it with radio-reflecting metal sheets, and use that as their telescope. The massive fixed dish at Arecibo is in some sense descended from this.

It took them three months to dig out a pit about 65 feet across (a bit under 22 meters, actually). It was nine feet deep. To smooth out the shape, they packed it with ash that was being dumped by a nearby power station. "They had to dump it somewhere so they were quite pleased that someone would take it away," Slee later explained to New Scientist.

When completed, it was the second-largest radio telescope in the world. It had three times the resolution of the telescope array that they used at work.

After completing a number of successful runs with the telescope, they revealed its existence to their bosses, who were so pleased that they provided supplies and funding to make it even larger and to improve its reflecting surface.

With a new member of their team, Dick McGee, they surveyed the area believed to include the center of the galaxy, using a frequency of 400 MHz. They were able to pick out a number of distinct radio sources, including one called Sagittarius A that they concluded was galactic center.

In 1958, only five years later, the Astronomical Union concurred, and established this point as the center of their astronomical mapping system.

The hole-in-the-ground telescope was in operation for only a couple of years but, in addition to finding galactic center, it detected radio waves from the Crab Nebula, a star that Chinese astronomers saw explode in 1054, and listened as two galaxies collided.

"Making the first discoveries in the world made us feel pretty special," Slee said modestly.

This amazing lunchtime project has long since been covered over, though visitors to Dover Heights in Sydney can see a replica that has been established in its place.

Astronomers continue to pinpoint the precise galactic center; it is known to be within Sagittarius A, and the most popular candidate today is a position within that source called Sgr A*.

New Scientist, 13 September 2003
Sydney Morning Herald, 21 July 2003

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