ABSTRACT
For a long time it has been known that there is a background noise present in a radio receiver which, no matter how perfect the components or how far the receiver may be removed from any source of terrestrial radio emission, can never be entirely eliminated. The reasons for this excess of background crackle were extensively investigated during the early days of radio communication and as early as 1926 Jansky in America began experiments in sweeping the sky in the hope of solving the problem of this irreducible noise. Two years of intensive research led him to the conclusion that part of this static was due to Hertzian waves reaching the Earth from outer space. By 1935 he was able to employ aerials which were far more directional in their reception and he discovered that the intensity of the noise increased as the aerials were moved progressively in the direction of the Milky Way and, moreover, that the maximum intensity was produced when they were pointed towards the galactic centre, in the region of Sagittarius.
