The cosmos possesses a wealth of different systems, ranging from the more obvious local objects such as the sun, planets and asteroids, and then the more distant stars and nebulae, to more subtle manifestations such as stellar winds, various ionized or neutral gas clouds, and exotic, compact stars. Many are present in the Milky Way, which forms the lens for our brief foray into the astrophysics of the cosmos. At left is an optical image of the Horsehead nebula and its environs.

The course begins with an exploration of the objects in the solar system. The focal point here is the ancient astronomical science of celestial mechanics, which was how astronomers first discovered the rich diversity of cosmic neighbors. Planetary motions will be explored, as will tidal forces, and properties of comets and asteroids, and the rings of Saturn will be touched upon. Extrasolar planet searches will be discussed. On the right is one of Cassini's stunning images of Saturn's rings during its recent rendezvous.

In order to study cosmic systems in some depth, we must apply various concepts from physics. While celestial mechanics was grounded in classical mechanics and Newton's theory of gravitation, 20th Century physics ushered in quantum mechanics, relativity and powerful new tools for astronomical exploration. Much of modern astronomical research, whether it focuses on the radio, optical, X-ray or gamma-ray wavebands, is built upon spectroscopic analysis. ASTR 350 devotes considerable time to elements of photometry, thermal physics, atomic spectroscopy and ionization balance to elucidate principal techniques for probing the physics of cosmic systems. Here the sequence of atomic transitions for hydrogen is depicted.

Having assembled a requisite body of physics, the course now studies solar and stellar spectra and inferences concerning the nature of their atmospheric layers. Both continuum and line features provide insight on various properties, including the fundamental characteristic that stellar interiors are much hotter than their atmospheres. Astronomical tools such as spectral classification and the Hertzsprung-Russell diagram will be addressed. To the right is displayed the solar spectrum in different optical wavebands, highlighting the prominence of absorption lines.

The focus is next on the larger structure of the sun and stars, exploring their hydrostatic equilibrium, phenomena such as convection, and the physics of their deep interiors via consideration of the elements of nucleosynthesis. This portion of the course exhibits why and for how long stars shine, thereby providing the most essential energy resource for life on Earth. Concepts from solar physics such as the solar cycle, solar neutrinos, the coronal regions and the solar wind are briefly explored. The image to the left is a SOHO UV picture of the sun that traces He emission at and above its surface.

While all stars are born young, like humans, they age and eventually die. Our serendipitous view of the cosmos now provides a snapshot survey of a host of different stellar epochs. The course now turns its attention to the study of stellar evolution, encompassing star formation via gravitational collapse of gas clouds, through evolution on the main sequence to giant and supergiant phases. The material differentiates between the life paths of low mass main sequence stars like the sun and much more massive stars that evolve rapidly. An image of the planetary nebula NGC6543 is depicted at right.

The course naturally progress to the late stages of stellar evolution and the death of stars. This focus explores phenomena such as stellar pulsation, eruptions and associated mass loss, planetary nebulae, and the final catastrophic destruction of a star as a supernova. These phases are an important component of the matter redistribution in, and life-cycle of, the Universe. The remnants of supernovae are briefly discussed. At left is the fascinating X-ray view of the Cassiopeia A supernova remnant provided by the Chandra X-ray Observatory.

The course wraps up with an "inescapable" foray into the exotic world of post-main-sequence stars. The study of compact objects, namely white dwarfs, neutron stars and black holes boggles the mind, providing a showcase for early 20th Century physics. The lectures outline the role of quantum degeneracy pressure in stabilizing white dwarfs and neutron stars against gravitational collapse, identifying the fundamental Chandrasekhar mass limit for each. Manifestations of neutron stars such as the pulsar phenomenon are explored, before the course progresses to the ultimate end state of matter, black holes, and Einstein's theory of General Relativity. To the right is a melange of the optical (Hubble Space Telescope) and X-ray (Chandra X-ray Observatory) images of the Crab pulsar wind nebula.