He found his special discipline soon: Spectroscopy, where he was the pioneer. He discovered dark-line spectra (Lines of some Fixed Stars, 1863), and in 1864 he examined the spectrum of a planetary nebula, NGC 6543 in Draco, and found that it had a bright line or emission line spectrum, namely the two greenish lines which could not be identified as of any known element at that time, and were then assigned to a new hypothetical element, "Nebulium." He therefore concluded correctly that this nebula was not composed of stars, which have a continuous spectrum, but of glowing gas. On May 18, 1866 he made the first spectroscopic observation of a nova, Nova Coronae 1866, and found emission lines of Hydrogen. In 1868 he took the spectrum of a comet and identified the spectral lines of ethylene in this spectrum.

He married in 1875, and his wife became a most active collaborator in his work. In 1899, they published a fine Atlas of Representatice Spectra; this work was awarded the Actonian Prize of the Royal Institution. Huggins published numerous papers in the Philosophical Transactions and other journals, which were re-published in 1909 as his collected Scientific Papers.

Sir William Huggins passed away on May 12, 1910.

Honors of Sir William Huggins include naming a Moon Crater (41.1S, 1.4W, 65 km diameter, in 1935) and a Mars Crater (49.4S, 204.4W, 90 km, in 1973) after him. Asteroid No. 2635 was named Huggins, discovered February 21, 1982 by E. Bowell at Anderson Mesa and provisionally designated 1982 DS; it also has a longer list of pre-discovery sightings labelled 1935 CB, 1942 FM, 1952 FZ, 1952 HP, 1953 PW, 1953 RS, 1957 WS, 1970 RQ and 1975 AB1.

Deepsky Discoveries In a series of papers, Huggins published his spectroscopic discoveries:

• 1864:
  • Line spectra (gaseous nebulae): H IV.37 (NGC 6543), Struve 6 (NGC 6572), H IV.73 (NGC 6826), H IV.51 (NGC 6818), H IV.1 (NGC 7009), M57, H IV.18 (NGC 7662), M27.
  • Continuous spectra (clusters and galaxies): M92, H IV.50 (NGC 6229), M31, M32, 55 And (GC 428; found stellar), H IV.26 (NGC 1535).
• 1865:
  • Line spectrum (nebula): M42.
  • Continuous spectra (clusters): M15, M2.
• 1866:
  • Line spectrum (nebulae): H IV.27 (NGC 3242), Struve 5 (NGC 6210), M17, H IV.16 (NGC 6905), H VI.38 (NGC 6804), H II.705 (NGC 7354), H I.192 (NGC 7008), M76, M97.
  • Continuous spectra (clusters and galaxies): H V.18 (M110), H I.151 (NGC 524), H I.156 (NGC 1023), M81, M82, M51, H V.43 (M106), M63, M3, H I.215 (NGC 5866, M102), h 1945 (NGC 6049, found stellar), M13, M12, H IV.50 (NGC 6229), M10, M14, H II.199 (NGC 6517), M11, H I.47 (NGC 6712), Auw N. 44 (GC 4473, NGC 6760), M56, h 2081 (NGC 6934), H I.52 (NGC 7006), H V.15 (NGC 6960), H II.207 (NGC 7217), H I.53 (NGC 7331), H II.233 (NGC 7332), H II.251 (NGC 7448), H II.212 (NGC 7457).

• William Huggins, 1904 Bruce Medalist

• William Huggins and W.A. Miller, 1864. On the Spectra of some of the Fixed Stars. Philosophical Transactions of the Royal Society of London, Vol. 154 (1864), p. 413-435.
• William Huggins and W.A. Miller, 1864. On the Spectra of some of the Nebulae. Philosophical Transactions of the Royal Society of London, Vol. 154 (1864), p. 437-444.
• William Huggins, 1865. On the Spectrum of the Great Nebula in the Sword-handle of Orion. Philosophical Transactions of the Royal Society of London, Vol. 155 (1865), p. 39-42.
• William Huggins, 1866. Further Observations on the Spectra of some of the Nebulae, with a Mode of determining the Brightness of these Bodies. Philosophical Transactions of the Royal Society of London, Vol. 156 (1866), p. 381-397.

• Kenneth Glyn Jones, 1991. Messier's Nebulae and Star Clusters. 2nd ed, Cambridge University Press, p. 326.