The determination of stellar ages has been - and still is - crucial for the development of our understanding of the universe, and to constrain theoretical models for the formation of galaxies and the evolution of planetary systems. Stellar ages provide scientists with timescales, and these timescales allow us to identify the relevant physical processes responsible for the development of cosmic structures. This book describes in a simple, yet rigorous, manner the vast array of techniques that have been developed and are currently being used to determine the ages of stars. It also explores how stellar ages inform our knowledge about planets, star clusters, galaxies, even distant galaxies that we cannot resolve into individual stars. Up-to-date with the latest research and technologies in the field, it includes the cutting-edge methods being used based on asteroseismology and discusses open problems that remain to be pondered in future research. It will be of interest to advanced undergraduates and graduate students studying astronomy, in addition to the general public. Key Features Presents an entertaining and accessible approach whilst also providing a rigorous and comprehensive presentation of the subject Describes how to unveil the ages of stellar populations in distant galaxies that we cannot resolve into individual stars Contains historical notes about these techniques, outstanding major problems, and a discussion on future developments in the field

In a unique collaboration, Nature Publishing Group and Institute of Physics Publishing have published the most extensive and comprehensive reference work in astronomy and astrophysics. This unique resource covers the entire field of astronomy and astrophysics and this online version includes the full text of over 2,750 articles, plus sophisticated search and retrieval functionality and links to the primary literature. The Encyclopaedia's authority is assured by editorial and advisory boards drawn from the world's foremost astronomers and astrophysicists. This first class resource is an essential source of information for undergraduates, graduate students, researchers and seasoned professionals, as well as for committed amateurs, librarians and lay people wishing to consult the definitive astronomy and astrophysics reference work.

In this Symposium, researchers specializing in pulsation, rotation, magnetic fields and stellar winds are brought together for the first time in order to broaden our understanding of O and B stars. Thanks to advances in digital spectroscopy, new types of pulsating B stars have been discovered. The pulsations can be understood in terms of the recent revision of metal opacities, but the effects of rapid rotation and magnetic fields need further study. Observations in the UV and X-ray regions demonstrate that many B and Be stars show other activity, besides pulsation which is not yet understood. The reason for the enhanced mass loss in Be stars is a question which dominates the Symposium and which remains unanswered, although it is surely to be found in activity at or near the photosphere coupled with rotation. It is shown that the geometry of the circumstellar envelopes around Be stars is indeed a flattened disk as they can now be optically resolved. The variability of radiatively-driven winds from O and B stars are likely related to the rotation of the star. This underlines the central theme of the book: that the various phenomena seen in these stars cannot be studied in isolation.

This book is designed for upper division courses in astronomy and as a reference for science professionals. The subject areas of astronomy and astrophysics have grown tremendously during the last few decades. New developments in radio astronomy and recent data retrieved from NASAs Hubble Space Telescope have resulted in many discoveries and created new interest in the study of the universe. Using four-color throughout, Astronomy & Astrophysics describes the different techniques and instruments employed in the study of the universe and the results obtained with discussion on both theory and observation. The book covers topics such as, minor planets, radio astronomy, astronomical telescopes, measurement of solar brightness distribution, black holes, and the Einstein effect. A CD-ROM with color figures and simulations accompanies the book.

Fundamental unsolved problems of stellar astrophysics include the effects of angular momentum on stellar structure and evolution, the nature and efficiency of the processes by which angular momentum is redistributed within and lost from stars, and the role that stellar rotation plays in enhancing or driving stellar mass loss. There appears to be a qualitative change in the nature and efficiency of these mechanisms near spectral type FO: hotter (more massive) stars typically retain more angular momentum at least until they reach the main sequence, while cooler stars typically spin down quickly. For the hotter stars, recent work suggests a strong link between the type of pulsation behavior, the mass loss rates, and the rotation velocity. If the same mechanisms are able to drive mass loss from the main sequence A stars, as has recently been proposed, then the current interpretations of a number of observations will be drastically affected: e. g. the ages of clusters may be incorrect by up to a factor of two, and the surface abundances of isotopes of He, Li and Be may no longer give constraints on cosmological nucleosynthesis. There are also effects on the evolution of the abundances of elements in the interstellar medium and on the general evolution of populations of stars. Thus the questions of the mechanisms of angular momentum and mass loss of stars more massive than the sun is important not only for stellar studies but for the foundations of much of modern astrophysics.