Galactic Central, a collection of floating cities in a vast, manmade, planetless cloud. Scout Shannon longed to see it since she first heard of it. This place long represented her shining future. But in her less shiny present, she reaches it by smuggling herself aboard a cargo ship and hides in the lower sewer-like levels of the most opulent of the floating cities. Teams of girl assassins still hunt her. Worse, her friends are in danger and don't even know. Scout has to save her friends, because saving her friends means saving her entire planet from enslavement to the Tajaki trade dynasty. Caught between two sides of that dynasty, with a mysterious third party desperate to remove her from the galaxy, Scout is in way over her head. But with her friends, she just might see a path to victory for all of them. "At Galactic Central" the sixth and final book in "The Travels of Scout Shannon" series, a young adult science fiction novel for fans of plucky heroines, girl assassins, political intrigue, and loyal dog sidekicks.

Now in a new, revised edition, the fourth book of the Nebula Award-winning author's Galactic Center series is a classic tale of man's future and fate--and the greatest mystery from outer space that humanity has ever encountered. Piloting an ancient starship, Killeen and the Bishop tribe escape the mech-ruled world of Snowglade. Seeking refuge on a far away planet, they discover vast wonders-an organic life-form as large as a world, a planet-coring cosmic string, a community of humans ruled by a brutal tyrant, and ultimately an alien race more awesome than any they have encountered. As they battle for survival against these myriad dangers, Killeen and his crew will gain an unforeseen ally-one that may determine humanity's true destiny...

This is the first comprehensive treatment of active galactic nuclei--the cosmic powerhouses at the core of many distant galaxies. The term active galactic nuclei refers to quasars, radio galaxies, Seyfert galaxies, blazars, and related objects, all of which are believed to share a similar central engine--a supermassive black hole many times the mass of the Sun. Astrophysicists have studied these phenomena for the past several decades and have begun to develop a consensus about many of their properties and internal mechanisms. Julian Krolik, one of the world's leading authorities on the subject, sums up leading ideas from across the entire range of research, making this book an invaluable resource for astronomers, physicists interested in applications of the theory of gravitation, and graduate students. Krolik begins by addressing basic questions about active galactic nuclei: What are they? How can they be found? How do they evolve? He assesses the evidence for massive black holes and considers how they generate power by accretion. He discusses X-ray and g-ray emission, radio emission and jets, emission and absorption lines, anisotropic appearance, and the relationship between an active nucleus and its host galaxy. He explores the mysteries of what ignites, fuels, and extinguishes active galactic nuclei, and concludes with a general review of where the field now stands. The book is unique in paying careful attention to relevant physics as well as astronomy, reflecting in part the importance of general relativity to understanding active galactic nuclei. Clear, authoritative, and detailed, this is crucial reading for anyone interested in one of the most dynamic areas of astrophysics today.

The third novel in the award-winning author's classic Galactic Center series is available once again. "A challenging, pacesetting work of hard science fiction that should not be missed" (Los Angeles Times). Nearly 100,000 years after first contact with the machines that dominate the universe, a few hundred humans survive. Trapped on Snowglade, a barren world near the center of the galaxy, people like Killeen of Family Bishop and his child Toby are primitive scavengers, homeless and hunted by the ruling "mechs." Then suddenly, a strange cosmic entity-neither organic nor cybernetic nor living matter-reaches out from a black hole to speak with Killeen. But can this fallen descendant of starfarers understand this alien being in time-and seize his only chance to save his family and mankind from final annihilation?

From the Nebula Award-winning author comes a newly revised edition of this story in his classic Galactic Center series. 2076: Technology has propelled the world into a new age of enlightenment. Nigel (from In the Ocean of Night) has left Earth to explore space for alien life. But while on this captivating mission, humanity's birthplace has fallen prey to attack and its seas are seeded with alien lifeforms. Now, Nigel is left to search for the only savior he knows-the one who saved him once before-the alien machine called the "Snark." Having left the solar system and turned traitor to its alien masters, Nigel is unsure of the Snark's new allegiance. Is the Snark a friend? Or will it also turn on Nigel... proving to be a deadly foe?

The Nebula Award-winning author's fifth installment of his classic Galactic Center series is reissued in this special edition that contains a teaser chapter from The Sunborn. Trying to escape the relentless mechs, the last humans from planet Snowglade take their ancient starship on a dangerous course straight into the Eater, the black hole at the galactic center. Hungry and desperate, the refugees begin to question the leadership of Captain Killeen, who believes the center holds their one hope of survival. Meanwhile, Killeen's son Toby struggles with the microchips that were implanted in his spine-a technology that now threatens his sanity. Caught between their genocidal pursuers and peril in the galactic center, Killeen and Toby bring humanity to its final destiny.

Our knowledge of the environment of the nucleus of our galaxy has been greatly enhanced, by more extensive and sensitive observations at radio and infrared wavelengths, the advent of high resolution x-ray imaging and spectroscopy, and considerable theoretical activity to understand the nucleus and its components, and their activity. The Galactic Center Workshop 2002 was organized to review recent research on the galactic center, including the latest state-of-the-art observations and important theoretical developments. The workshop covered phenomena on scales ranging from the central several hundred parsecs to the central parsec and within. Each topic was approached from both multi-wavelength observational and theoretical perspectives.

The present book is a translation of the original German edition (published in 1982) with some minor corrections and improvements. The guide to sup plementary and advanced literature given in the Appendix, however, has been brought up to date. This book is addressed primarily to students taking astronomy as a prin cipal or subsidiary subject, and to scientists of related fields, but amateur as tronomers should also be able to profit from it. For most chapters an elementary knowledge of mathematics and physics will be sufficient, however, Chaps. 5 and 6 impose somewhat greater requirements. In addition the reader should already be acquainted with the basic concepts of stellar physics as treated in introduc tory books, including the spectral types, the system of stellar magnitudes and colours, absolute magnitudes and luminosities, the Herlzsprung-Russell dia gram and its interpretation. A modem textbook should use SI units. On the other hand, the use of the cgs system is still the prevailing custom in astrophysics - together with the special units of astronomy: length is quoted in parsecs [pc], mass in solar masses [M0] and time in years [a]. We have therefore compromised and employed both cgs and SI units in this book, whichever was the appropriate choice in each instance. A table for conversion of cgs units into SI units and vice versa is given in the Appendix.

The investigation of the Galactic nucleus and its surroundings is necessarily a modem endeavor, for traditional observations made at visual wavelengths have not even begun to penetrate the veil of -30 magnitudes of visual extinction that intercedes. On the other hand, infrared, and especially radio observers find a relatively unobstructed view of the central portion of the Galaxy, so the study of this arena has proceeded apace with the development of these branches of astronomy. Thus, it is no accident that the first IAU sponsored conference to be held on the Galactic center is timed to coincide with the initiation, or the immediate aftennath, of major technical developments at long wavelengths, including infrared array detectors, millimeter-wavelength aperture synthesis, and self-calibration and refmed deconvolution algorithms in aperture synthesis radio astronomy. The center of the Galaxy is also accessible to X and gamma-ray observers, and progress at high energies has been steady, especially as imaging capabilities are being realized at X-ray wavelengths. However, one might expect that the revolution in the high energy domain is still ahead of us, as instruments with larger collecting areas and improved spatial resolution are now being developed. The youth of this subject is evidenced by the relatively small number of meetings that have been devoted to it.

Having escaped yet another closing trap, Scout Shannon finds herself on a snowbound mountaintop far from civilization. With assassins eager to kill her, laying low on an alien world is the smartest play. But wherever Scout goes, trouble follows. And a hamlet in the mountains gets far more remote when girl assassins destroy the only means back to civilization. Now Scout and her dogs face a long, cold climb back to the frozen star port city, her only guide, a girl whose sister Scout killed when fighting for her life. Can she get to safety before the girl learns the truth about Scout? And what secrets of her own is this strange girl keeping? "Over Freezing Altitudes" the fifth book in "The Travels of Scout Shannon" series, a young adult science fiction novel for fans of resourceful heroines, survival in extreme environments, girl assassins and loyal dog sidekicks.