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Early Radio Astronomy

Grote Reber's telescope, Wheaton, Illinois, 1937
Image courtesy NRAO/AUI/NSF

In 1936, an amateur astronomer named Grote Reber built a radio telescope in his backyard. His was the first telescope ever built specifically to receive radio waves from the sky. Over the next several years, he pointed his telescope all over the sky, and discovered many new sources of radio waves. One of the sources he found, Cygnus A, would prove to change the course of modern astronomy.

Fifteen years later, in 1951, astronomers Walter Baade and Rudolph Minkowski found the object that created Cygnus A's radio emissions. They used the 200-inch visible-light telescope on Mount Palomar in California to find an unusual-looking galaxy. But when they looked at the spectrum of the galaxy, they found an even greater surprise.

Cygnus A turned out to be a galaxy with a redshift of 0.057. This redshift measurement put it over 700 million light years from Earth, the most distant object yet observed. For Reber to detect its radio source from 700 million light years away, Cygnus A had to be the most intense radio source ever seen.

Cygnus A
Image courtesy NRAO/AUI/NSF
Observers: P.A.G. Scheuer, R.A. Laing, R.A. Perley

As the years progressed, astronomers found more radio sources that corresponded to distant galaxies. Eventually, they started to find radio sources that appeared to correspond to stars! Stars are not a strong source of radio waves, so astronomers knew they were seeing something very unusual.

Let's take a look at some of these unusual objects.