Download or read book An Absorption-line Study of the Galactic Neutral-hydrogen at 21 Cm written by Michael Paul Hughes and published by . This book was released on 1971 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: The paper describes observations of galactic 21-cm line absorption in the spectra of ninety-seven radio sources made with the two-element interferometer at the Owens Valley Radio Observatory. Measurements of 21-cm absorption are of fundamental importance because they yield directly information on the optical depth of the galactic hydrogen. Almost all of the many studies of the 21-cm line are concerned with observations in emission, and require assumptions concerning the optical depth before the data can be interpreted in terms of the temperature or columnar density of the gas.