Fig. 1.2 Karl Jansky and his rotating Bruce Array known as the “merry-go-round,” which he used in 1932 to detect radio emission from the Milky Way Galaxy. Credit: NRAO/AUI/NSF
During the summer and autumn of 1930, Karl used his rotating array to determine the direction of arrival of signals from transmitting stations in England and South America and easily detected static from nearby thunderstorms.10 In November he became aware of static coming from a direction where there was no obvious weather disturbance, but apparently much of Jansky’s time during his period was spent on other activities (Southworth 1956). Following an overhaul of his receiving system, he began in the summer of 1931 to keep more systematic records of displayed static on a running paper chart recorder (Fig. 1.3). During the 1931/1932 winter, after the summer thunderstorm activity had subsided, he noted that the anomalous noise was highly peaked in a direction that appeared to move with the time of the day, being strongest in the morning toward the east, toward the south at noon, and toward the west late in the afternoon. Jansky naturally concluded that it had something to do with the Sun, and wrote to his parents, “That would be interesting wouldn’t it?”11 Coincidently, in December the Sun lies in the direction of the Milky Way, and over the following months the peak noise came earlier each day, and Jansky noted that it was well removed from the Sun. However, he apparently did not yet realize that the source was extraterrestrial.
