This 6th edition of "Tools of Radio Astronomy", the most used introductory text in radio astronomy, has been revised to reflect the current state of this important branch of astronomy. This includes the use of satellites, low radio frequencies, the millimeter/sub-mm universe, the Cosmic Microwave Background and the increased importance of mm/sub-mm dust emission. Several derivations and presentations of technical aspects of radio astronomy and receivers, such as receiver noise, the Hertz dipole and beam forming have been updated, expanded, re-worked or complemented by alternative derivations. These reflect advances in technology. The wider bandwidths of the Jansky-VLA and long wave arrays such as LOFAR and mm/sub-mm arrays such as ALMA required an expansion of the discussion of interferometers and aperture synthesis. Developments in data reduction algorithms have been included. As a result of the large amount of data collected in the past 20 years, the discussion of solar system radio astronomy, dust emission, and radio supernovae has been revisited. The chapters on spectral line emission have been updated to cover measurements of the neutral hydrogen radiation from the early universe as well as measurements with new facilities. Similarly the discussion of molecules in interstellar space has been expanded to include the molecular and dust emission from protostars and very cold regions. Several worked examples have been added in the areas of fundamental physics, such as pulsars. Both students and practicing astronomers will appreciate this new up-to-date edition of Tools of Radio Astronomy.

This 6th edition of "Tools of Radio Astronomy", the most used introductory text in radio astronomy, has been revised to reflect the current state of this important branch of astronomy. This includes the use of satellites, low radio frequencies, the millimeter/sub-mm universe, the Cosmic Microwave Background and the increased importance of mm/sub-mm dust emission. Several derivations and presentations of technical aspects of radio astronomy and receivers, such as receiver noise, the Hertz dipole and beam forming have been updated, expanded, re-worked or complemented by alternative derivations. These reflect advances in technology. The wider bandwidths of the Jansky-VLA and long wave arrays such as LOFAR and mm/sub-mm arrays such as ALMA required an expansion of the discussion of interferometers and aperture synthesis. Developments in data reduction algorithms have been included. As a result of the large amount of data collected in the past 20 years, the discussion of solar system radio astronomy, dust emission, and radio supernovae has been revisited. The chapters on spectral line emission have been updated to cover measurements of the neutral hydrogen radiation from the early universe as well as measurements with new facilities. Similarly the discussion of molecules in interstellar space has been expanded to include the molecular and dust emission from protostars and very cold regions. Several worked examples have been added in the areas of fundamental physics, such as pulsars. Both students and practicing astronomers will appreciate this new up-to-date edition of Tools of Radio Astronomy.

Einleitung und Inhaltsi.ibersicht . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Die Struktur und Geschwindigkeitsverteilung der interstellaren Materi- eine Ubersicht . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 . . . . . . . . . . . . . . . . 2. Der Zusammenhang der Intensitat der 21-cm-Linie mit Dichte und Temperatur des interstellaren Mediums . . . . . . . . . . . . . . . . . . . . 19 . . . . . . . . 3. Die V erteilungsfunktion der kinetischen Wolkentemperaturen . . . . . . . 23 . A. Die V erteilung der StoBzeiten . . . . . . . . . . . . . . . . . . . . . . . 24 . . . . . . . . . . B. Die Abki.ihlungsfunktion des interstellaren Gases . . . . . . . . . . . . . 29 . . . . C. Die Verteilung der Wolkentemperaturen . . . . . . . . . . . . . . . . . 31 . . . . . . . 4. Dichtebestimmung bei endlichem Winkelauflosungsvermogen . . . . . . . 35 . . 5. Wolkenstruktur und Dichtebestimmung . . . . . . . . . . . . . . . . . . . . 40 . . . . . . . . 6. Ein Poisson-Modell der Wolkenverteilung 43 Literaturverzeichnis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 . . . . . . . . . . . . . . . 5 Summary One of the main tasks of 21-cm investigations consists in the determination of the density of interstellar Hydrogen gas. This has usually been done with the assumption that the Hydrogen gas forms a stratum of more or less uniform density. If Hydrogen clouds exist, they were believed to be transparent for the 21-cm radiation, and the density gradients were supposed to be small. However, in the last years observations accumulated which indicate this picture to be incorrect. The interstellar material seems to be concentrated in clouds of rather high density and considerable opacity but of small diameter. The kinetic temperatures of these clouds need not to be the same for all clouds, in the contrary, rather large temperature variations are indicated. These facts make it necessary to reconsider the derivation of the formulae connecting the measured intensity of the 21-cm radiation with the density of the Hydrogen gas and the kinetic temperature. This paper intends to lead to an improvement for the solution of this problem.