It might be surprising, but two of the most important discoveries in radio astronomy were made by accident. Maybe just as surprisingly, by engineers investigating radio communication issues, not "real" astronomers.
Back in the 1930s, the new technology of radio offered for the first time the possibility of easy, worldwide communication. However, before this technology could be offered commercially, prospective companies needed to investigate its feasibility. Would interference disrupt the service? How often? What mitigation would be possible?
Bell was one of the companies planning to offer radio communication services, so it gave one of its engineers, Karl Jansky, the task of investigating any interference issues liable to cause significant disruptions. To do this, Jansky built an antenna, and mounted it on the wheels from a discarded Model T Ford, so that it could be rotated to determine arrival direction of the interference.
Over the following weeks and months Jansky catalogued interference from car ignition systems, electric motors and other devices, thunderstorms, power lines and other radio transmitters. When he had identified all these, he was left with something odd, a faint hissing in the headphones. He rotated the antenna to determine the direction the hiss was coming from. Then he found something really odd, as time passed the direction of maximum hiss moved slowly westward. At that time the sun was in the sky during the measurements, and with his antenna not being very directional, he thought he might be getting radio emissions from the sun. This would have been a discovery anyway, because to that point no solar radio waves had been detected, or even expected to be there.
However, a few months later that emission was turning up at night, and Jansky concluded the hiss was actually radio emissions from the Milky Way.
The astronomical community did not receive the news well. Firstly, they thought that all the electromagnetic emission coming from space would be due to the heat of the stars, coming to us directly or being reradiated or reflected by cosmic clouds of dust. If this were the case, the radio emissions would be very weak, and not worth bothering with, especially with the technology available at the time.
The second reason, which illustrates one of the less nice aspects of human nature, they saw Jansky as not an approved member of their community, and suggested he should stick to playing with his radios.
Fortunately, Grote Reber, a radio amateur, heard about Jansky's discovery and built the first radio telescope, launching radio astronomy.
The accidental second discovery was made in the 1960s. At the time NASA was running Project Echo. This involved putting large balloons made of aluminium foil into space, with the intention of bounding radio communication signals off them. For these tests a horn antenna, looking rather like a huge ear trumpet, was set up for the purpose.
Two engineers, Arno Penzias and Robert Wilson, were given the task of evaluating the test system. During the tests they found something odd. Just as Jansky did, they found a bit more signal than they expected. It came from all over the sky and was equivalent to a temperature of about 3.5 Kelvins.
In this case astronomical recognition was immediate, because Robert Dicke and his team had been calculating whether we can detect any trace of the Big Bang today, and estimated that it would be a radio emission equivalent to a temperature of about 3.5 Kelvins.
However, before they had time to look for it, Dicke heard what Penzias and Wilson had found, and said to his colleagues "We've been scooped!!".
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The planetary parade will be fully in place on the 28th. Look after sunset. Mercury will have sneaked up into the after-sunset glow, with Saturn close by. Moving to the left, that is eastward, find brilliant Venus, then Jupiter, almost as bright; and Mars, conspicuously red. The moon will reach First Quarter on the 6th.
Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory.
