The birth of radio astronomy | Life

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In the 1930s, radio communication opened up the world.

For the first time, it became technically possible for a person in any country to communicate with anyone else on the planet.

Companies were investing heavily in services to provide publicly accessible communications. However, experience has shown that shortwave radio (using wavelengths between about 100 and 10 meters) is vulnerable to interference and occasional radio outages. No one was going to invest in or use an unreliable communications network, so companies began researching what was affecting their communications and identifying possible workarounds.

One of the companies working on this new communications frontier was Bell in New Jersey. To help them design the new system, they entrusted one of their engineers, Karl Jansky, with the task of identifying the sources of interference likely to affect the new services. To do this, he built an antenna that was mounted on the wheels of a Ford Model T car, so that it could spin, scanning the horizon to see where different forms of interference were coming from. He attached this antenna to a then state-of-the-art radio receiver and began to work.

Over the next few months, he identified radio clutter from thunderstorms and other natural phenomena, as well as myriad forms of man-made interference.

Curiously, he found that when this interference was absent, he could hear a regular hiss, which disappeared if he disconnected the antenna. He scanned with the antenna and found the direction in which the hiss was loudest, and discovered, to his surprise, that during the day the interference peak moved from east to west. After months of work, he concluded that the culprit was the Milky Way, with the strongest signals coming from the direction of the constellation Sagittarius. Jansky had discovered cosmic radio waves, that the Milky Way is a radio source and that the strongest emissions come from the direction of the center of our galaxy.

One would expect such a discovery to shock the astronomical community, as at the time all astronomical observations were made using optical telescopes. However, the attitude of astronomers was that radio engineers should stick to playing with their radios and stop pretending to be scientists. Fortunately, Jansky’s discovery caught the attention of a radio ham named Grote Reber.

Reber had successfully spoken to radio amateurs on every continent of the world and was looking for a new challenge. Jansky’s discovery did the trick, and in his garden in Wheaton, Illinois, he built the world’s first radio telescope: a parabolic antenna nearly 10 meters in diameter, made of wood with a reflective sheet metal surface. of galvanized steel. After trying one receiver design after another, covering a wide range of wavelengths, he finally detected the emissions reported by Jansky. However, Reber had a great advantage, his antenna was designed to nod up and down, so he went on to make the first radio map of the sky, clearly showing the radio emissions from the Milky Way and that they were the most shining in the direction of the center of our galaxy.

Surprisingly, the astronomical community gave Reber the answer Jansky received.

Ironically, it was World War II that changed everything. Scientists and engineers were brought together to develop new devices for the war effort, and in the process mutual trust grew, and earlier results of radio astronomy, and some new accidental discoveries made during hostilities, established the new science. Then, at the end of the war, new technologies were used to make radio telescopes and radio astronomy was on the move.

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Before dawn, Saturn is low in the south, with Jupiter shining to the left, then Mars and finally Venus, low in the dawn glow. The moon will reach last quarter on the 20th.

Ken Tapping is an astronomer at the Dominion Radio Astrophysical Observatory of the National Research Council of Canada, near Penticton.

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