how long this can continue. Atomic and molecular data are not so well archived from an astrophysical viewpoint, and this needs to be remedied. We recommend that small, efficient data centers be established in atomic, molecular, and nuclear astrophysics by the appropriate agencies through the normal peer review process. The agencies should coordinate so as to avoid duplication of effort.
Theory performs a number of functions in the overall enterprise of astronomy. It provides the basic paradigm within which observations are framed and without which they degenerate into a catalog of uninterpreted data. At its most satisfying, theory makes predictions that are later verified by observation. Theory can also have dramatic impact in a "post-dictive" mode by explaining previously observed phenomena. It catalyzes specific observations, which in turn stimulate new model building in a mutually interactive enterprise that drives progress in the field. Finally, theory provides much of the conceptual stimulation that invests astronomy with excitement.
In assessing the impact of theory in the decade of the 1980's, it is important to bear in mind that the big payoff of successful predictions, explanations, or guiding frameworks may be a long term process, so that the successes of the 1980's often had seeds planted earlier. Likewise, the general activity in theory in the 1980's may not bear fruit until the 1990's or beyond. In the following discussion, paragraphs marked with "*" highlight verified predictions.
In the solar system, the Voyager spacecraft provided dramatic proof or illustrations of a number of theoretical concepts, including tidal heating as a cause of vulcanism, and density waves and shepherd satellites in planetary rings. Further impressive accomplishments were compelling explanations of Jupiter's great red spot, the Kirkwood gaps, and the apparently chaotic rotation of Saturn's satellite Hyperon.
Observations of the vibrational spectrum of the Sun led to the new science of helioseismology, with a firm theoretical basis that was rapidly developed. Models of the rotation of the solar interior based on the observed rotational splitting in the spectrum overturned previous conceptions of rotation on cylinders, but a fully self-consistent model that will account for the 11 (22) year solar cycle is still being sought in ongoing work. Continuing studies of solar neutrinos included new suggestions of induced mixing of neutrino types and the possible effects of hypothetical new particles. This work continues within a fundamental theoretical framework laid down in the 60's and 70's. The Sun is predicted to have a magnetic heliosphere, and Pioneer 10 and the Voyagers continue to search for the heliopause.
The conceptual notion that impacts of massive extraterrestrial bodies may have led to major biological extinctions illustrates the strong linkages that can develop between apparantly unrelated disciplines, and the importance that apparently arcane theoretical studies (for example, the structure and dynamics of the Oort cometary cloud) can suddenly have for other subject areas (for example, the environmental consequences of a major impact may be similar to the effects of nuclear winter). In the broadest context, work in this area has led to the recognition that the solar system is a dangerous and unpredictable place, and that astronomical catastrophes are likely to have had a profound influence on the developments and survival of life on Earth.
Significant progress was made in the study of the interstellar medium (ISM) and star formation. Large structures in the ISM—supershells and superbubbles—with diameters of hundreds of parsecs were successfully modelled as being due to correlated supernovae in stellar associations, although for some structures—particularly the largest ones—this model has some difficulty. Observations of the diffuse ISM continue to be interpreted in light of a three-phase model developed in the 70's, in which the ISM is divided into cold (T ~ 102K), warm (T ~ 104K), and hot (T ~ 106K) phases in approximate pressure equilibrium. In the last decade, debate raged as to the pervasiveness of the hot component of the ISM and on the relative importance of magnetic fields in determining the observed structure of the ISM. The discovery of small dust grains and polycyclic aromatic hydrocarbons through infrared observations led to extensive theoretical study