The cosmology sector of the course begins with a discussion of the cosmological principle, the fundamental axiom that underpins the global structure of the universe. Then it moves to cosmochronology, the dating of distant objects and epochs in the universe. As a prelude to the fuller discussion of the spacetime of the universe, Newtonian cosmology is studied now, defining the essential structure of the expansion of the universe subsequent to the Big Bang, without being encumbered by the mathematical formalism associated with general relativity. This weak field limit suffices to identify key elements of a matter-dominated universe such as the critical closure density, which demarcates criteria for open and closed universes. On the left is a schematic for the array of cosmological possibilities for the evolution and fate of the universe. The present age of the universe and the acceleration/deceleration of the expansion depend on the values of the matter density and the cosmological constant. (From Astronomy Today, by Chaisson & McMillan).

The fuller formalism of relativistic cosmology is now advanced, prefaced by an entree of general relativity. This then introduces the students to the Robertson-Walker metric, and the Friedman equation. Solutions for both matter- and radiation-dominated universes are explored to identify the concept of the Big Bang, which pre-dated the discovery of the CMB by over 3 decades. Einstein's famous cosmological constant is introduced, employed by him to explain the near-Euclidean character of our space. Then we connect to the real universe by expounding upon observables such as the lookback time, angular diameters and inferred luminosities, as they appear to us, as functions of the redshift to a source. This sets the scene for a study of supernova cosmology at redshifts z~0.1-1, the first tool to determine that the Hubble expansion is accelerating, thereby promoting the need for a repulsive force on cosmological scales that has been annointed "Dark Energy." On the right is a pie chart for the current determination of the make-up of the universe, based on supernova probes at moderate redshifts and the power spectrum of fluctuations in the cosmic microwave background radiation.

The smoking gun for evidence of the Big Bang is the cosmic microwave background radiation (CMB), the relic of the early universe when the matter was decoupling from light. This forms the next focus of the course, starting with its discovery, determination of its blackbody form, dipolar anisotropy as evidence of the peculiar motion of the solar system, and the full-blown power spectrum of angular fluctuations as determined recently by the WMAP experiment. Diagnostics using CMB polarization measurements will be discussed. Its existence rules against steady-state universes, and its dappled appearance in sky maps (click here for the WMAP sky distribution) signals the onset of structure formation in the universe. Accordingly, this rich physical manifestation of the universe dating from over 13 billion years ago has garnered two Nobel Prizes in physics. The power-spectrum of angular fluctuations in the CMB, as measured recently by the Wilkinson Microwave Anisotropy Probe (WMAP: see the WMAP Media Outreach Page), is depicted on the right.

The final chapter in our cosmology saga concerns the history and evolution of the universe. This focuses first on the thermal history since the Big Bang, transitioning from the radiation-dominated to the matter-dominated epoch. The first 3 minutes is not just a catchphrase here, but defines the era when the nucleosynthetic status quo was effectively established. The principal interactions in primordial nucleosynthesis and the roles of deuterium and lithium in probing the matter content of the universe are identified. The eras of recombination and last scattering also form a focus, followed by a brief foray into the gravitational perturbation physics of structure formation. Finally, the course will venture into the exotic world of inflation, the postulate for the rapid expansion of the quantum soup that constituted the extremely early universe. This theory has recently garnered excitement again with the topical evidence for propulsion of the universe's expansion by a mysterious form of Dark Energy. At right, a depiction of the evolution of the expanding universe, highlighting the rampant "explosion" during the inflationary epoch, the comparatively stable era of structure and galaxy formation up to the present time, where acceleration of the expansion has now become profound. From the WMAP Media Outreach Page.

Having established the framework for the greater structure and evolution of the Universe, we now turn to a guided tour of its more discrete entities, and the development of our understanding of the extragalactic frontier. The Universe is truly diverse in terms of its constituents, and our closest host, the Milky Way galaxy, is a fascinating and fairly representative place to start our exploration of the greater cosmos. This portion of the course begins with a description of the morphology of the Milky Way, namely the spatial distribution of constituent stars, gas and dust, defining the disk, bulge and halo. The material will also touch upon the Galactic fountain model, the Magellanic Stream, and the tool of gravitational microlensing, all in relation to the halo. On the left is the 21cm composite sky map from the NRAO Image Gallery, in galactic coordinates, illustrating the distribution of neutral hydrogen in the Milky Way.

The kinematics of the Milky Way forms the next focus, covering how peculiar velocities provide information concerning the global motion of the Galaxy. We will discuss the Oort model of galactic rotation and in particular how the rotation curve provides a profound indication for the existence of dark matter. Then our attention will turn to the fascinating Galactic Center region, a rich and dynamic environment that is strongly influenced, if not powered, by the presence of a supermassive black hole. Keplerian evidence for the existence and mass estimation of this black hole will be presented, a technique widely employed in various extragalactic contexts. The course will describe molecular and radio structures near the Center, and touch upon recent discoveries in the X-ray band. At right is a 20cm Very Large Array (VLA) radio image (from the NRAO Image Gallery) of the Sagittarius A region at the Galactic Center, displaying the prominent continuum arc.

Next, the nature of galaxies is explored. Spirals, ellipticals, the Hubble sequence and Hubble's famous tuning-fork diagram. Freeman's law, the Tully-Fisher relation and velocity dispersion diagnostics are highlighted. An exploration of spiral structure ensues, focusing on the dynamics of density wave theory, which is also applicable to modeling Saturn's rings. The course also summarizes ensemble observational properties of ellipticals, their luminosity functions, and briefly discusses the King profile for their matter distribution. A combined Hubble Space Telescope/Spitzer Space Telescope image of the Sombrero Galaxy (M104) from the Spitzer Image Gallery is depicted on the right.

Galactic evolution and the larger scale structure of the Universe form the next focus. A descriptive introduction to interactive galaxies is provided, moving to key elements of galaxy formation, drawing upon dynamical analogs with star formation from gas clouds in our own galaxy. Determinations of the extragalactic distance scale and the critical Hubble's law for cosmic expansion are addressed; these are essential underpinnings for the cosmology components that were studied in the first half of the course. This section concludes with a discussion of clusters of galaxies and gas therein, and larger structure in the distribution of visible matter in the universe, elucidated via various extensive and deep sky surveys such as the classic Harvard CfA redshift one in the optical waveband. To the right is an optical/IR montage of the Antennae galaxies NGC 4038 and NGC 4039 in collision, highlighting stars and molecular gas (blue); it was obtained from the NRAO Image Gallery. Close-up images of impressive detail can be found at the HubbleSite Image Gallery.

Among the most exotic and powerful sources in the universe are active galaxies. Our studies conclude with an outline of the key features of Seyferts, radio galaxies, BL Lac objects and blazars, and quasars, the most powerful variety that reside at the greatest distances. Powered by disk accretion, their central engines are supermassive black holes, whose environs are called active galactic nuclei (AGNs). These sources often exhibit luminous, collimated jets of relativistic gas outflow, and in the case of radio galaxies, also enormous lobes of radio emission that signify dissipation on almost intergalactic scales. Characteristics of the accretion disks and jets will be discussed, including the properties of apparent superluminal motion and short timescale variability in radio, optical, X-ray and gamma-ray bands. A brief diversion to the analogous galactic phenomenon of microquasars will be made. The geometrical unification model of Seyferts and blazars will be addressed, followed by an exposition on how distant quasars can be used to probe the nature of the intergalactic medium. A Very Large Array (VLA) image of the radio galaxy 3C 130 at 20cm from the NRAO Image Gallery is depicted on the left.