The Herschel 400 is a list of 400 galaxies, nebulae and star clusters, picked from over 2,500 deep-sky objects discovered and catalogued by the great eighteenth-century astronomer Sir William Herschel and his sister Caroline. It comprises 231 galaxies, 107 open clusters, 33 globular clusters, 20 planetary nebulae, 2 halves of a single planetary nebula and 7 bright nebulae. In this guide Steve O'Meara takes the observer through the list, season by...