Monday, June 16, 2008

A Telephone Man Tunes In

The first true radio astronomer was not trained as an astronomer at all. Even to this day, many astronomers who work in the radio regime were trained as physicists and electrical engineers, and later learned to apply their knowledge to astronomy. Karl Jansky, the son of a Czech immigrant who settled in Oklahoma (where Karl was born in 1905), took a degree in physics at the University of Wisconsin. After graduating, Karl went to work in 1928 not as an astronomer, but as a telephone engineer with Bell Labs. The phone company was looking for ways to make telephone communications possible with shortwave radio, but the transmissions were bedeviled by all sorts of interference.
Now most people hadn’t given much thought to radio static. After all, static was something to be avoided if possible—meaningless noise that only interfered with communications. Jansky was given the assignment of studying sources of static at a wavelength of 14.6 m in an effort to track down the precise sources of radio interference and eliminate them.
On a farm in Holmdel, New Jersey, not far from Bell Labs, Jansky set up a very ungainly looking device, which he called a merry-go-round. It was a large directional antenna, which looked rather like the biplane wing of the Wright brothers’ first airplane. It was mounted on some discarded Model T Ford wheels and could be rotated through 360 degrees by means of a motor. Using this contraption, Jansky was soon able to identify all the known sources of radio interference except one. Jansky tracked the stubborn and mysterious interference. When amplified and sent to a speaker, the interference sounded like a faint hiss. The source seemed to be in the sky, since Jansky could track it rising and setting with the stars. But it wasn’t coming from just anywhere in the sky. By the spring of 1932, Jansky traced the primary source of radio noise to the direction of the constellation Sagittarius, which astronomers Harlow Shapley and Jan H. Oort had identified (from the distribution of globular clusters in the Galaxy) as the direction of the center of the Milky Way Galaxy. Using his merry-go-round antenna, Jansky had “discovered” the center of the much bigger merry-go-round that is our galaxy. There were other sources of radio noise in the sky as well, but Jansky noted that the sun itself was not an impressive source of radio noise. This observation was a bit surprising, since the sun is so close to us. He concluded that whatever the source of radio noise, it probably wasn’t distant stars.
Jansky published his “discovery” late in 1932, and the detection of radio signals from space appeared in national newspapers by the following year. Strangely enough, Jansky himself didn’t pursue the science he had accidentally created. As for most professional astronomers, they continued to look through only one of their two windows, the portion of the spectrum available to optical telescopes. It took another nonastronomer, Grote Reber, to appreciate the possibilities of what Jansky had discovered. In today’s image-conscious world, we might call Reber a nerd. But as the example of Bill Gates has shown us, some nerds go on to change the world. Born in Wheaton, Illinois in 1911, he grew up tinkering with radio transmitters, building one powerful enough to communicate with other ham radio operators all over the world. Like many early radio astronomers, he became an electrical engineer, but never lost his interest in amateur radio, and when he read about Jansky’s discovery, he tried, without success at first, to adapt his own shortwave receiver to pick up interstellar radio waves with wavelengths of 10 cm.
He tinkered with the electronics (trying longer wavelengths), and, in 1937, built a paraboloidal antenna 30 feet in diameter. With this, Reber not only confirmed Jansky’s discovery of radio waves from the direction of Sagittarius, but found other sources in the direction of the constellations Cygnus, Cassiopeia, and elsewhere.
Reber confirmed that the radio signals did not coincide with the positions of visible stars. Directing his dish toward such bright stars as Sirius, Vega, or Rigel, he detected nothing. But looking toward a starless area in Cassiopeia, he picked up strong radio waves. He had unknowingly detected a supernova remnant known as Cassiopeia A.

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