Table of Contents

1. Time-Pre 20th Century 2. Solar Time 3. Ephemerides 4. Variable Earth Rotation 5. Earth Rotation and Polar Motion 6. Ephemeris Time 7. Relativity and Time 8. Dynamical and Coordinate Time Scales 9. Clock Developments 10. Microwave Atomic Clocks 11. Optical Atomic Standards 12. International Atomic Time (TAI) 13. Definition and Role of a Second 14. Coordinated Universal Time 15. Time in the Solar System 16. Time and Frequency Transfer 17. Modern Earth Orientation 18. International Activities 19. Time Applications 20. Future of Timekeeping

About the Author

Dennis D. McCarthy worked in the Time Service and Earth Orientation Departments of the U. S. Naval Observatory (USNO) for the past 40 years, reaching the position of Director of Time at USNO. He has been involved in both the improvements in time keeping and time transfer, and the advances in the observational determination, analyses and prediction of accurate Earth orientation. Dr. McCarthy is the author of a large number of papers on time scales and Earth orientation. P. Kenneth Seidelmann worked in the Nautical Almanac and Orbital Mechanics Departments of the U. S. Naval Observatory for 35 years, reaching the level of Director of Astrometry at USNO. He has been involved in the development of astronomical ephemerides, relativistic dynamical time scales, space missions, and the applications of improved astrometric accuracy. He is currently a Research Professor at the University of Virginia. Professor Seidelmann is editor of the 'Explanatory Supplement to the Astronomical Almanac', coauthor of 'Fundamentals of Astrometry', and author of a large number of papers on fundamental astronomy.