The material given in this 'Introduction to astronomical photometry' is the subject matter of a lecture at the University of Geneva. It is, therefore, intended for those students, physicists or mathematicians, who have completed their bachelor's degree or diploma, and are intending to work for their Ph.D. in astronomy. We assume then the elementary ideas of astrophysics, magnitude, colour index, spectral classes, luminosity classes, gradient, atmospheric extinction are already known. The student may find it useful to re-read the work of Schatzman [1], Dufay [2] and Aller [254] before embarking upon the study of this 'Introduction to astronomical photometry'. It is not our aim in this book to deal with every aspect of stellar photometry. On the contrary, we shall restriet ourselves to looking at subjects ofwhich knowledge seems to us essential for someone who has to use photometrie quantities in his astronomical research. We are, therefore, keeping the interests of the photometrie measurements user partieularly in mind. We shall only discuss very superficially the technical prob lems and reduction methods for atmospheric extinction. These problems are dealt with very clearly in Astronomical Techniques [3]; the first by A. Lallemand, H. L.

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1. General Definitions and Energy Distribution for Various Spectral Types.- 1.1. Definition of Photometric Measurement, A Special Case of Astronomical Measurement.- 1.2. Description of the Energy Distribution in Stellar Spectra.- 1.3. Characteristic Physical Parameters of the Continuous Energy Distribution.- 1.4. Characteristic Parameters of the Energy Distribution.- 1.5. The Importance of Lines in Photometric Measurement.- 1.6. Distribution of the Fraction of Energy Absorbed in the Lines.- 1.7. The Importance of Accuracy when Making Measurements in Astronomical Photometry.- 1.8. Interstellar Absorption Law Deduced from Spectrophotometry.- 2. Photometric Measurements, Effects of Bandwidths and Interstellar Absorption.- 2.1. Characteristic Parameters of a Photometric System.- 2.2. Atmospheric Extinction Correction. Role of the Bandwidth.- 2.3. Effect of Bandwidth on Corrections for Interstellar Extinction.- 2.4. Effects of the Bandwidth and the Form of Extinction Law on Ratios of the Type Eu/Ey.- 2.5. Effects of Various Extinction Laws and Bandwidths on Ratios of the Type Av/Ey.- 2.6. Relationships between Heterochromatic Magnitudes Obtained from Two Similar Systems.- 2.7. Relationships between the Colour Indices of Two Similar Photometric Systems.- 2.8. Comparison oF The Ratios Eu/Ey and Av/Ey for Two Similar Photometric Systems.- 3. Two-Dimensional Photometric Representations of Stars.- 3.1. Relationship between Colour Indices and Gradients.- 3.2. Colour Index and the Balmer Discontinuity.- 3.3. Two-Dimensional Photometric Representation of Stars: Introduction to the UBV System.- 3.4. Interstellar Reddening Lines in the UBV Diagram.- 3.5. Position of the Black-Body and other Radiation Laws in the UBV Diagram.- 3.6. Effect of Binarity in UBV Diagrams.- 3.7. Dispersion Caused by Rotation.- 3.8. Blocking and Blanketing Effects inUBV.- 4. Multi-Colour and Wide-Band Photometry.- 4.1. Comparison between the UBV and RGU Systems.- 4.2. Information Growth by Increasing the Number of Passbands.- 4.3. Description of Energy Distributions Using a Photometry Having n Wide Passbands.- 4.4. Use of Multi-Colour Photometric Systems in Describing the Interstellar Extinction Law.- 4.5. Introduction of Linear Combinations of Indices.- 4.6. Linear Combination of Heterochromatic Indices and Interstellar Extinction Effects.- 4.7. The Q Parameter of theUBV System.- 4.8. The [d], [?] and [g] Parameters of the U B V B1B2V1G Photometric System.- 5. Intermediate and Narrow Passband Photometry.- 5.1. Introduction.- 5.2. Narrow Band Photometry, Centred upon Hydrogen Lines.- 5.3. Narrow Band Photometry Centred upon Hydrogen Lines.- 5.4. Narrow Band Photometry Centred upon Lines and Bands other than Hydrogen.- 5.5. Intermediate Passband Photometry.- 5.6. Intermediate Passband Photometry.- 5.7. Intermediate Passband Photometry.- 5.8. Intermediate Passband Photometry.- 5.9. Intermediate Passband Photometry.- 5.10. Notes on Narrow and Intermediate Band Photometry of Molecular Bands and Groups of Lines.- 6. Photometric Parameters and their Correlation With Basic Parameters Describing the Physical State of Stellar Atmospheres.- 6.1. Introduction.- 6.2. Effective Temperature Parameters.- 6.3. Effective Temperature and Gravity Using Models - Case of Hot Stars.- 6.4. Adjustment of Models Using Colour Indices.- 6.5. Determination of the Shape of the Passbands of Intermediate and Wide Filter Systems.- 6.6. Notes on the Fitting of Models Using Colour Indices.- 6.7. Discussion of the Properties of a Photometric System Using Stellar Atmosphere Models. Vectorial Representation.-6.8. Calibration of Photometric Diagrams.- 6.9. Calibration of Photometric Diagrams.- 6.10. Calibration of Photometric Diagrams.- 7. Photometry Applied to Various Stellar Objects.- 7.1. Introduction.- 7.2. O Star Photometry.- 7.3. A Few Remarks about the Photometry of Ap Stars and Their Variability.- 7.4. Sub-Dwarf Photometry.- 7.5. Peculiar Cool Stars, such as Barium, CH and Carbon Stars.- 7.6. Cool Star Photometry.- 7.7. UBV Diagrams of some other Objects; QSS, White Dwarfs, Seyfert Nuclei, N Galaxies, Pulsars.- 7.8. Photometry of Galaxies.- 7.9. Photometry of Globular Clusters.- 7.10. On the Photometry of RR Lyrae-Type Variables.- 7.11. UBV Photometry of the Sun.- 7.12. Photometric Catalogues and Bibliographic Notes.- Index of Names.- Index of Subjects.