Essential Radio Astronomy (ERA) grew from lecture notes for the one-semester radio astronomy course taken by all astronomy graduate students at the University of Virginia. To attract advanced undergraduates with backgrounds in astronomy, physics, engineering, or astrochemistry to radio astronomy, we limited the prerequisites to basic physics courses covering classical mechanics, macroscopic thermodynamics, electromagnetism, and elementary quantum mechanics. Prior courses covering electromagnetism with vector calculus, electrical engineering, special relativity, statistical thermodynamics, advanced quantum mechanics, Fourier transforms, or astrophysics were not required. Nearly everything in ERA has been derived from first principles in order to fill the gaps in students’ backgrounds and make ERA a useful reference for practicing radio astronomers.

Classical radio astronomy textbooks such as Radio Astronomy by J. D. Kraus emphasized radio engineering and were written for two-semester courses that prepared students for careers in radio astronomy. In this era of multiwavelength astronomy, most graduate students can afford to spend only one semester studying radio astronomy, during which only the most essential concepts can be presented. Our goal is to give them the background needed to read and understand the radio astronomy literature, to recognize when radio observations might help solve an astrophysical problem, and to design, propose, and analyze radio observations. The ERA textbook complements the longer and more technical Tools of Radio Astronomy textbook) that “describes the tools radio astronomers need to pursue their goals” in greater detail. ERA was also shaped by our belief that radio astrophysics owes more to thermodynamics than to electromagnetism, so Kirchhoff’s law appears more frequently than Maxwell’s equations.

Originally, our brief lecture notes were printed and handed out to students in the traditional classroom environment: a chalk-dusted professor covered blackboards with equations which students faithfully copied into their notebooks for later study. To avoid this unnecessary work and free the students to concentrate on the ideas being presented, we expanded the abbreviated notes into complete texts with figures and full mathematical derivations, then converted them from TeX to html so they could be posted to the web and projected onto a screen in any classroom. Now the professor faces “heads up” students who can watch, listen, and ask questions without worrying about failing to write down a crucial step in some long derivation.

A broader goal of the National Radio Astronomy Observatory¹ is fostering the community of researchers using radio astronomy by attracting and training the most talented university students anywhere in the world. NRAO directors Paul Vanden Bout, Fred Lo, and Tony Beasley have generously supported our efforts to upgrade and expand all of the course materials (lectures, problem sets, exams) that are now available on this website. (The original but now obsolete web version can still be found here.

We hope that the combination of this book and its associated website will facilitate teaching radio astronomy at the university level, especially at the many colleges and universities lacking “black belt” radio astronomers. The website can display large galleries of color images, link to interactive demonstrations and relevant articles on the web, present problem sets and solutions, and be updated frequently to present new findings or report errata from the book. We thank Princeton University Press for agreeing to a nonexclusive copyright that allows the book and website to coexist.

NRAO, Charlottesville James J. Condon jcondon@nrao.edu 2016 March 12 Scott M. Ransom sransom@nrao.edu