Corrections

November, page 36—Because of a composition error two lines were transposed from one column of text to another. The affected paragraphs should have read:

A number of other processes in space are radio emitters—molecular rotational transitions excited by collisional impact and free–free transitions in ionized gas, to name twoand —radio astronomy as a consequence is both “high energy” and “low energy,” “relativistic” and “chemical,” with a phenomenology extremely rich compared to that of most bands of the electromagnetic spectrum. Radio waves have been detected from nearly every class of object known to astronomy at the time of Jansky’s discovery—including the Sun, Moon, planets, stars, gaseous nebulae, supernova remnants and normal galaxies—and radio investigations have revealed entirely new objects without which modern astrophysics would hardly exist: neutron stars, molecular clouds, quasars, radio galaxies, and the cosmic microwave background. The Nobel Prize in physics has been awarded to four radioastronomers who participated in these discoveries—in 1974 to Martin Ryle for work on the extragalactic sources and to Anthony Hewish for the discovery of pulsars (neutron stars), and in 1978 to Arno Penzias and Robert W. Wilson for the discovery of the microwave background.

As a result of these accomplishments, radioastronomy has grown into one of the main subdivisions of observational astronomy. Nearly 30% of the observational papers in the leading astronomical journals are based on radio data, and there are large radio observatories in over a dozen countries, with major new facilities under construction or planned by Australia, Britain, Canada, France, Germany, Japan and the United States.

page 38—The photo in figure 2 is printed upside down, so that the companion of M51 is in the lower part of the photo instead of at the top. The editors regret these errors.