This book is an outgrowth of the notes made for the semester lectures on 'Problems of Extragalactic Astronomy' given almost annually during two decades at the Ob servatorio Astronomico of the Universidad de Cordoba. Shorter versions were also given at La Plata, Santiago de Chile, Sao Paulo, Rio de Janeiro and Paraiba. E. Scalise made a Portuguese language version of the notes and encouraged me to publish them; although my friend J. Kleczek is to be blamed for the idea of this book. Not every subject on Extragalactic Astronomy has been touched in this book: instead I have followed those which interested me during 25 years of professional practice in this part of the world. I acknowledge helpful suggestions from M. Pastoriza and G. Carranza, the com prehension of Director L. Milone, and the collaboration of the staff of the Observa tory in Cordoba. R. Tschamler's humor and wit made light the task of producing the English version and M. Pizarro's devotedness produced the edited MS. To both of them I am in deep gratitude. "A book is published out of necessity, otherwise the author would spend his entire life polishing the originals" was the answer given by J. L. Borges to an inquisi tive journalist. These words explain why this book is so different from the lecture notes, and also from the book I was hoping for. I thank B. McCormac and the D. Reidel Publ. Co. for my salvation from Borges' inferno.

Inhalt
I: Forms and Structures.- 1.1. Normal and Peculiar Galaxies.- 1.2. Classification of Normal Galaxies.- 1.3. Apparent and True Flattening of Galaxies.- 1.4. Other Classifications Systems.- 1.5. Classification of Peculiar Galaxies.- II: Normal Galaxies.- II.1. Contents.- II.1.1. Photometric Properties.- II.1.2. Stellar Content.- II.1.3. The Interstellar Medium in Galaxies.- II.1.4. Subsystems.- II.2. Motions and Masses.- II.2.1. Kinematics.- II.2.2. Masses of Galaxies.- II.2.3. Mass-Luminosity Ratios.- II.3.2. Evolution of Galactic Content.- III: Active Galaxies.- III.1. Classification.- III.2. Intergalactic H II Regions (IG H II).- III.3. Galaxies with Nuclear Emission (neG).- III.4. Irr II Galaxies.- III.5. Seyfert Galaxies (SyG).- III.5.1. Spectrum of Emission.- III.5.2. Continuum Spectrum.- III.5.3. Variability.- III.5.4. Radioemission.- III.5.5. Correlations.- III.6. Strong Radio Galaxies (SRG).- III.6.1. Radio Structures.- III.6.2. Spectrum of Radio Frequencies.- III.6.3. Time Scale.- III.6.4. Compact Sources.- III.6.5. Optical Forms Associated with SRG's.- III.6.6. Optical Spectra.- III.6.7. Energetics of SRG's.- III.7. N Galaxies.- III.8. Quasi Stellar Objects (QSO).- III.8.1. Continuum Spectrum.- III.8.2. Line Spectrum.- III.8.3. BL Lacertae Objects.- III.8.4. Redshifts and Nature of the QSO's.- III.9. Activity in Compact Objects.- III.9.1. Excitation Mechanism.- III.9.2. The Source of Energy.- IV: Galaxies and their Environment.- IV.1. Tidal Interactions.- IV.1.2. Non-tidal Interactions.- IV.2. Agregates of Galaxies.- IV.2.1. Pairs and Multiplets.- IV.2.2. Groups of Galaxies.- IV.2.3. Clusters.- IV.2.4. Second Order Clustering.- IV.2.5. Clustering.- IV.3. Mean Mass Density of Matter in the Universe.- V: Measuring the Universe.- V.1. Distance Indicators.-V.1.1. Primary Distance Indicators.- V.1.2. Other Photometric Indicators.- V.1.3. Geometric Indicators.- V.1.4. Other Indicators.- V.2. The Scale of Distances.- V.2.1. The Hubble Flow.- V.2.2. The Quest for H0.- V.3. Far Away and Long Ago.- V.3.1. TheRedshift.- V.3.2. The Hubble Law.- VI: Cosmology.- VI.1. Basic Assumptions.- VI.2. Explosive Cosmologies.- VI.3. Thermal Evolution of the Universe.- VI.4. Primaeval Nucleosynthesis.- VI.5. The Background Radiation.- VI.6. Observational Cosmology.- VI.6.1. Observable Parameters.- VI.6.2. Fitting the Model to the Universe.- VI.6.3. Lifting the Restriction ? = 0.- VII: Gravitational Instability and Galaxy Formation.- VII.1. Theory of Jeans' Wavelength and Mass.- VII.1.1. The Jeans Mass.- VII.2. Gravitational Instability in an Expanding Universe.- VII.2.1. The Era of Gravitational Instability.- VII.3. Protogalaxies.- VII.3.1. Non-linear Growth of a Density Perturbation.- VII.4. Galaxy Formation Through Dissipative Collapse.- VII.4.1. Stationary State out of Equilibrium.- VII.4.2. Hierarchy of Fragmentations.- VII.4.3. The End of the Hierarchy.- VII.4.4. Global Dynamics.- VII.4.5. The Influence of Rotation.- VI.5. Dissipationless Collapse.- VIII: Notes and Comments.- VII.1. Catalogs and Atlas of Galaxies.- VIII.2. Composite Spectra.- VIII.3. The H I Spectrum.- VIII.4. Determination of Rotation Curves.- VIII.5. Rotation Period of Central Regions in Galaxies.- VIII.6. Note for Section V.1.3.