An introduction to radio astronomy, 4th edition: by B. F. Burke, F. Graham-Smith and P. N. Wilkinson, Cambridge, Cambridge University Press, 2019, 540 pp., £59.99 (hardback), ISBN 9781107189416. An introduction to radio astronomy, 4th edition, by B. F. Burke, F. Graham-Smith and P. N. Wilkinson Cambridge, Cambridge University Press, 2019, 540 pp., £59.99 (hardback), ISBN 9781107189416. Designed specifically for imaging supermassive black holes, EHT is a very long baseline interferometry (VLBI) array consists of a network of eight radio telescopes, essentially the largest aperture in the world. [Extracted from the article]