The 19th century saw an unprecedented expansion of known objects in the universe. William and Caroline Herschel conducted a comprehensive search of northern skies with telescopes powerful enough to resolve many nebulae into star clusters. Their achievements include the discovery of Uranus in 1781, and the publication of a catalog of 2,500 nebulae and star clusters in 1802. William’s son, John Herschel, published an expanded catalog in 1864. Further expanded by John Dreyer, it was reissued in 1888 as the New General Catalogue of Nebulae and Clusters (NGC), containing 7840 deep sky objects.