Famous for his metal prosthetic nose, and for being associated with 'unlucky' days in Scandinavian folklore, Tycho Brahe (1546-1601) made the most accurate naked-eye astronomical measurements of his day. Cataloguing more than 1,000 new stars, his stellar and planetary observations helped lay the foundations of early modern astronomy. John Louis Emil Dreyer (1852-1926) was a fellow Dane, but he spent much of his working life in Ireland. When he was fourteen, he had read a book about Brahe and this inspired him to 'be an astronomer and nothing else'. First published in 1890, Dreyer's biography of his hero remained the definitive work for more than a century. He sets out to illuminate not simply the life of his subject, but also the lives and work of Brahe's contemporaries and the progress of science in the sixteenth century.