▪ Abstract Although we have a general understanding of the manner in which individual stars form, our understanding of how binary stars form is far from complete. This is in large part due to the fact that the star formation process happens very quickly and in regions of the Galaxy that are difficult to study observationally. We review the theoretical models that have been developed in an effort to explain how binaries form. Several proposed mechanisms appear to be quite promising, but none is completely satisfactory.

▪ Abstract This review discusses three main topics: evolution to the ultra-compact (UC) state; the properties of UC HII regions and their environments; and UC HII regions as probes of Galactic structure. The evolution to UC HII regions begins in giant molecular clouds that provide the natal material for prestellar cores that evolve into hot cores, the precursors of UC HII regions. The properties of each evolutionary phase are reviewed, with particular emphasis on those of hot cores. The observed properties of UC HII regions and their environments are summarized with emphasis on the physical processes that may produce the observed properties. The final section summarizes the use of UC HII regions as probes of Galactic structure: in particular, the Galactic population and distribution of newly formed massive stars, the location of spiral arms, and the average galactocentric temperature and abundance gradients.

▪ Abstract I fled with my parents from Hitler's Austria to Australia and studied physics at Sydney University. I obtained my Ph.D. in quantum electrodynamics with Rudolf Peierls at Birmingham University and came to Cornell to work with Hans Bethe. I have stayed at Cornell ever since, and I have essentially had only a single job in my whole life, but have switched fields quite often. I worked in nuclear astrophysics and in late-stellar evolution, estimated the Initial Mass Function for star formation and the metal enrichment of the interstellar medium. I suggested black hole accretion as the energy source for quasars, worked on molecule formation on dust grain surfaces, and was involved in 21-cm studies of gas clouds and disk galaxies. I collaborated with my wife on the neurobiology of the neuromuscular junction and with one of my daughters on the epidemiology of tuberculosis.

▪ Abstract The formation and evolution of galaxies is one of the great outstanding problems of astrophysics. Within the broad context of hierachical structure formation, we have only a crude picture of how galaxies like our own came into existence. A detailed physical picture where individual stellar populations can be associated with (tagged to) elements of the protocloud is far beyond our current understanding. Important clues have begun to emerge from both the Galaxy (near-field cosmology) and the high redshift universe (far-field cosmology). Here we focus on the fossil evidence provided by the Galaxy. Detailed studies of the Galaxy lie at the core of understanding the complex processes involved in baryon dissipation. This is a necessary first step toward achieving a successful theory of galaxy formation.

▪ Abstract Radio astronomy has provided evidence for the presence of ionized atmospheres around almost all classes of nondegenerate stars. Magnetically confined coronae dominate in the cool half of the Hertzsprung-Russell diagram. Their radio emission is predominantly of nonthermal origin and has been identified as gyrosynchrotron radiation from mildly relativistic electrons, apart from some coherent emission mechanisms. Ionized winds are found in hot stars and in red giants. They are detected through their thermal, optically thick radiation, but synchrotron emission has been found in many systems as well. The latter is emitted presumably by shock-accelerated electrons in weak magnetic fields in the outer wind regions. Radio emission is also frequently detected in pre–main sequence stars and protostars and has recently been discovered in brown dwarfs. This review summarizes the radio view of the atmospheres of nondegenerate stars, focusing on energy release physics in cool coronal stars, wind phenomenology in hot stars and cool giants, and emission observed from young and forming stars.Eines habe ich in einem langen Leben gelernt, nämlich, dass unsere ganze Wissenschaft, an den Dingen gemessen, von kindlicher Primitivität ist—und doch ist es das Köstlichste, was wir haben.One thing I have learned in a long life: that all our science, measured against reality, is primitive and childlike—and yet it is the most precious thing we have. A. Einstein 1951, in a letter to H. Mühsam, Einstein Archive 36-610

▪ Abstract Cosmic microwave background (CMB) temperature anisotropies have and will continue to revolutionize our understanding of cosmology. The recent discovery of the previously predicted acoustic peaks in the power spectrum has established a working cosmological model: a critical density universe consisting of mainly dark matter and dark energy, which formed its structure through gravitational instability from quantum fluctuations during an inflationary epoch. Future observations should test this model and measure its key cosmological parameters with unprecedented precision. The phenomenology and cosmological implications of the acoustic peaks are developed in detail. Beyond the peaks, the yet to be detected secondary anisotropies and polarization present opportunities to study the physics of inflation and the dark energy. The analysis techniques devised to extract cosmological information from voluminous CMB data sets are outlined, given their increasing importance in experimental cosmology as a whole.

▪ Abstract The search for evidence of extraterrestrial intelligence is placed in the broader astronomical context of the search for extrasolar planets and biomarkers of primitive life elsewhere in the universe. A decision tree of possible search strategies is presented as well as a brief history of the search for extraterrestrial intelligence (SETI) projects since 1960. The characteristics of 14 SETI projects currently operating on telescopes are discussed and compared using one of many possible figures of merit. Plans for SETI searches in the immediate and more distant future are outlined. Plans for success, the significance of null results, and some opinions on deliberate transmission of signals (as well as listening) are also included. SETI results to date are negative, but in reality, not much searching has yet been done.

▪ Abstract The cosmic infrared background records much of the radiant energy released by processes of structure formation that have occurred since the decoupling of matter and radiation following the Big Bang. In the past few years, data from the Cosmic Background Explorer (COBE) mission provided the first measurements of this background, with additional constraints coming from studies of the attenuation of TeV γ-rays. At the same time, there has been rapid progress in resolving a significant fraction of this background with the deep galaxy counts at infrared wavelengths from the Infrared Space Observatory (ISO) instruments and at submillimeter wavelengths from the Submillimeter Common User Bolometer Array (SCUBA) instrument. This article reviews the measurements of the infrared background and sources contributing to it and discusses the implications for past and present cosmic processes.

▪ Abstract Rotation curves of spiral galaxies are the major tool for determining the distribution of mass in spiral galaxies. They provide fundamental information for understanding the dynamics, evolution, and formation of spiral galaxies. We describe various methods to derive rotation curves and review the results obtained. We discuss the basic characteristics of observed rotation curves in relation to various galaxy properties, such as Hubble type, structure, activity, and environment.

▪ Abstract During the last decade, the understanding of fine features of the structure and evolution of stars has become possible as a result of enormous progress made in the acquisition of high-quality observational and experimental data, and of new developments and refinements in the theoretical description of stellar plasmas. The confrontation of high-quality observations with sophisticated stellar models has allowed many aspects of the theory to be validated, and several characteristics of stars relevant to Galactic evolution and cosmology to be inferred. This paper is a review of the results of recent studies undertaken in the context of the Hipparcos mission, taking benefit of the high-quality astrometric data it has provided. Successes are discussed, as well as the problems that have arisen and suggestions proposed to solve them. Future observational and theoretical developments expected and required in the field are also presented.