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The controversial question of whether the majority of the narrow
absorption lines observed in QSO spectra represent cosmological
intervening systems or ejecta from the QSO themselves is settled.
QSO absorption line spectroscopy, initially a mere technique, has
matured into an essential extragalactic research tool for
understanding the content of the Universe at redshifts between 0
and 4, and beyond. The only previous important meeting devoted to
"QSO Absorption Lines" was held in May 1987 at the Space Telescope
Science Institute in Baltimore, Maryland, U.S.A. Since that time,
nearly a decade ago, research has been ex tremely active in this
now well-established field of astrophysics. Theoretical stud ies
and simulations have taken advantage of the constant progress in
computer technology, and during these last few years, the
observational results have bene fited largely from the new
facillities offered by the Hubble Space Telescope in the UV
wavelength range and the Keck Telescope for high-resolution
spectroscopy.
The observation, in 1919 by A.S. Eddington and collaborators, of
the gra- tational de?ection of light by the Sun proved one of the
many predictions of Einstein's Theory of General Relativity: The
Sun was the ?rst example of a gravitational lens. In 1936, Albert
Einstein published an article in which he suggested - ing stars as
gravitational lenses. A year later, Fritz Zwicky pointed out that
galaxies would act as lenses much more likely than stars, and also
gave a list of possible applications, as a means to determine the
dark matter content of galaxies and clusters of galaxies. It was
only in 1979 that the ?rst example of an extragalactic
gravitational lens was provided by the observation of the distant
quasar QSO 0957+0561, by D. Walsh, R.F. Carswell, and R.J. Weymann.
A few years later, the ?rst lens showing images in the form of arcs
was detected. The theory, observations, and applications of
gravitational lensing cons- tute one of the most rapidly growing
branches of astrophysics. The gravi- tional de?ection of light
generated by mass concentrations along a light path
producesmagni?cation,multiplicity,anddistortionofimages,anddelaysp-
ton propagation from one line of sight relative to another. The
huge amount of scienti?c work produced over the last decade on
gravitational lensing has clearly revealed its already substantial
and wide impact, and its potential for future astrophysical
applications.
The observation, in 1919 by A.S. Eddington and collaborators, of
the gra- tational de?ection of light by the Sun proved one of the
many predictions of Einstein's Theory of General Relativity: The
Sun was the ?rst example of a gravitational lens. In 1936, Albert
Einstein published an article in which he suggested - ing stars as
gravitational lenses. A year later, Fritz Zwicky pointed out that
galaxies would act as lenses much more likely than stars, and also
gave a list of possible applications, as a means to determine the
dark matter content of galaxies and clusters of galaxies. It was
only in 1979 that the ?rst example of an extragalactic
gravitational lens was provided by the observation of the distant
quasar QSO 0957+0561, by D. Walsh, R.F. Carswell, and R.J. Weymann.
A few years later, the ?rst lens showing images in the form of arcs
was detected. The theory, observations, and applications of
gravitational lensing cons- tute one of the most rapidly growing
branches of astrophysics. The gravi- tional de?ection of light
generated by mass concentrations along a light path
producesmagni?cation,multiplicity,anddistortionofimages,anddelaysp-
ton propagation from one line of sight relative to another. The
huge amount of scienti?c work produced over the last decade on
gravitational lensing has clearly revealed its already substantial
and wide impact, and its potential for future astrophysical
applications.
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