The Department of Astrophysical Sciences offers advanced training in astrophysics. The faculty and staff in the department conduct world-leading research in theoretical and computational astrophysics, observational astronomy, astronomical surveys, and instrumentation (both hardware and software). The fascinating discoveries of modern astronomy challenge the human understanding of the broadest possible range of physical phenomena. The graduate program in Astrophysical Sciences prepares students for scientific careers in astrophysics through a combination of classes and early and active participation in research projects, culminating in original thesis research.<br>Princeton has a long tradition in observational, numerical, and theoretical cosmology with research efforts in Physics, Astronomy and at the IAS. Princeton faculty helped develop today's standard cosmological model (Bahcall, Dunkley, Gott, J. Ostriker, Spergel, Steinhardt, Zaldarriaga) and helped introduce important concepts such as dark matter, dark energy, and inflation. Paul Steinhardt (physics) was not only a key figure in the development of the inflationary model, but has been recently developing its most promising alternative: the ekpyrotic universe. Princeton faculty are working on a diverse set of problems in theoretical cosmology: time travel (Gott), the topology of large-scale structure (Gott), the shape of the universe (Spergel), formation and evolution of galaxies and large-scale structure (Bahcall, J. Ostriker), clusters of galaxies and their use as cosmological tools (Bahcall, J. Ostriker), the distribution of dark matter (Bahcall, J. Ostriker), non-Gaussianities from the early universe (Spergel, Zaldarriaga), galaxy formation, and the physics of the IGM (Bahcall, J. Ostriker).