In 1948ΓÇöthe early days of radio astronomyΓÇötwo British astrono- mers, Sir Martin Ryle and F. Graham, discovered a strong radio source in the constellation Cassiopeia. They called the source Cassiopeia A. Other astronomers, using optical telescopes, attempted to locate the object visually, but found nothing. It was as if radio waves were emanating from empty space.
In 1951, with the help of the 200 inch Palomar telescope, astronomers W. Baade and R. Minkowski were able to identify a very faint, wispy nebula. Subsequent spectroscopic analysis indicated that the nebula had unusually strong concentrations of heavy elements. These concen- trations were the first clues that the
