Huggins built a private observatory at 90 Upper Tulse Hill, London, from where he and his wife carried out extensive observations of the spectral emission lines and absorption lines of various celestial objects. On 29 August 1864, Huggins was the first to take the spectrum of a planetary nebula when he analysed NGC 6543. He was also the first to distinguish between nebulae and galaxies by showing that some (like the Orion Nebula) had pure emission spectra characteristic of gas, while others like the Andromeda Galaxy had the spectral characteristics of stars. Huggins was assisted in the analysis of spectra by his neighbour, the chemist William Allen Miller. Huggins was also the first to adopt dry plate photography in imaging astronomical objects.