This well-schooled text provides a detailed description of how to perform practical astronomy or spherical astronomy. It is an authoritative source on astronomical phenomena and calendars.

The Explanatory Supplement to the Astronomical Almanac offers explanatory material, supplemental information and detailed descriptions of the computational models and algorithms used to produce The Astronomical Almanac, which is an annual publication prepared jointly by the US Naval Observatory and Her Majesty's Nautical Almanac Office in the UK. Like The Astronomical Almanac, The Explanatory Supplement provides detailed coverage of modern positional astronomy. Chapters are devoted to the celestial and terrestrial reference frames, orbital ephemerides, precession, nutation, Earth rotation, and coordinate transformations. These topics have undergone substantial revisions since the last edition was published. Astronomical positions are intertwined with timescales and relativity in The Astronomical Almanac, so related chapters are provided in The Explanatory Supplement. The Astronomical Almanac also includes information on lunar and solar eclipses, physical ephemerides of solar system bodies, and calendars, so The Explanatory Supplement expounds upon each of these topics as well. The book is written at a technical, but non-expert level. As such, it provides an important reference for a full range of users including astronomers, engineers, navigators, surveyors, space scientists, and educators.

This accessible reference presents the evolution of concepts of time and methods of time keeping, for historians, scientists, engineers, and educators. The second edition has been updated throughout to describe twentieth- and twenty-first-century advances, progress in devices, time and cosmology, the redefinition of SI units, and the future of UTC.

This new revision of a standard work gives a general but comprehensive introduction to positional astronomy. Useful for researchers as well as undergraduates.

The uses of time in astronomy - from pointing telescopes, coordinating and processing observations, predicting ephemerides, cultures, religious practices, history, businesses, determining Earth orientation, analyzing time-series data and in many other ways - represent a broad sample of how time is used throughout human society and in space. Time and its reciprocal, frequency, is the most accurately measurable quantity and often an important path to the frontiers of science. But the future of timekeeping is changing with the development of optical frequency standards and the resulting challenges of distributing time at ever higher precision, with the possibility of timescales based on pulsars, and with the inclusion of higher-order relativistic effects. The definition of the second will likely be changed before the end of this decade, and its realization will increase in accuracy; the definition of the day is no longer obvious. The variability of the Earth's rotation presents challenges of understanding and prediction. In this symposium speakers took a closer look at time in astronomy, other sciences, cultures, and business as a defining element of modern civilization. The symposium aimed to set the stage for future timekeeping standards, infrastructure, and engineering best practices for astronomers and the broader society. At the same time the program was cognizant of the rich history from Harrison's chronometer to today's atomic clocks and pulsar observations. The theoreticians and engineers of time were brought together with the educators and historians of science, enriching the understanding of time among both experts and the public.