Published online by Cambridge University Press: 25 April 2016
The subject of interstellar matter is one of the most active fields of astronomical research to-day. Observational information spans the full electromagnetic spectrum from long radio waves to gamma rays and includes cosmic-ray particles. Results of chemical research find as much application now as mathematical methods. Interstellar matter plays a leading role in galactic and extragalactic research, and contributes increasingly to stellar astronomy and in solar system studies.