An Introduction to Radio Astronomy 4th Edition

Book Preface

Astronomy makes use of more than 20 decades of the electromagnetic spectrum, from gamma-rays to radio. The observing techniques vary so much over this enormous range that there are distinct disciplines of gamma-ray, X-ray, ultraviolet, optical, infrared, millimetre, and radio astronomy. Modern astrophysics depends on a synthesis of observations from the whole wavelength range, and the concentration on radio in this text needs some rationale. Apart from the history of the subject, which developed from radio communications rather than as a deliberate extension of conventional astronomy, there are two outstanding characteristics of radio astronomy which call for a special exposition.

First, the astrophysics. Radio is essential for observing:

– ionized atmospheres of stars and interstellar plasma, penetrating dust and gas which often obscure other wavelengths;
– the processes of star and planet formation;
– molecules in cold interstellar clouds;
– hydrogen, the fundamental element in the Universe;
– pulsars, the most accurate clocks in the Universe;
– cosmic magnetic fields;
– the structure of the early cosmos.

Second, the techniques: low energy radio photons can be treated as classical waves. Hence, in contrast with other regimes, they can be coherently amplified and manipulated in complex receiver systems. Coherent amplification enables one to take account of the phase as well as the intensity of incoming waves, allowing the development of interferometers with the highest angular resolution in astronomy and the development of aperture synthesis, now realized in powerful new interferometric radio telescopes such as LOFAR, LWA, MeerKAT, MWA, ASKAP and ALMA, with the first phase of the Square Kilometre Array (SKA) impending. The basic techniques follow well-established principles, but the advent of massive computer power and broadband fibre optic communications has only recently brought these impressive instruments within the range of possibility. At the same time, existing radio telescopes, now including the new five-hundred metre FAST, using new receiver technology continue front-line research in several astrophysical domains, such as pulsars, fast radio bursts, and large area surveys for low-brightness emission. Fundamental cosmology has been transformed by observations of the cosmic microwave background from spacecraft and from the ground.

In view of the developments in the last ten years, this fourth edition of the book has been completely revised and reorganized. The new generation of radio telescopes, with dramatically improved performance, and new generations of astronomers, require a presentation which is a combination of fundamental principles, an exposition of the basics of telescope techniques, and a survey of the radio cosmos. Our rewriting has followed the advice of many colleagues, and we have provided references to recent reviews as well as to papers which represent the current state of the art. We are also providing on-line supplementary material, presenting a wide range of colour images and other material to complement the text. It will be available at www.cambridge.org/ira4.

We are aiming particularly at a graduate student audience attracted by radio astronomy with its new observational capabilities – in particular SKA, which will grow in size and power over the next two decades.

For the reader wishing to progress further in the subject there is a growing list of books at a more advanced level. Of these we particularly recommend: Interferometry and Synthesis in Radio Astronomy, A. R. Thompson, J. M. Moran, and G. W. Swenson (Springer).

Essential Radio Astronomy, J. J. Condon and S. M. Ransom (Princeton University Press). Tools of Radio Astronomy, T. L. Wilson, K. Rohlfs, and S. H¨uttemeister (Springer). Our intention is to provide an introduction which is useful both to the observer and to the astrophysicist; perhaps it will appeal most to those who, like ourselves, enjoy the membership of both categories