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.