Vacuum ultraviolet astrophysics

A brief historical review of the development of Vacuum Ultraviolet Astrophysics is given, which shows its tigh association with the development of space research. The scientific potential interests of making astrophysical observations in the far ultraviolet between the neutral hydrogen Lyman 912 A limit and 3,000 A, are described. The major outcomes of the most important astronomical satellites (in particular OAO-A, TD-1-A, and Copernicus) are reviewed, in the areas of the interstellar medium, stellar model atmospheres, chromospheres and coronae, stellar winds, mass loss, and ultraviolet observations of galaxies and quasars. These results illustrate the great wealth of ultraviolet astrophysics. Since Copernicus observations reveal that the density of neutral hydrogen in certain directions of our galaxy, and particularly in the vicinity of our solar system, is sometimes lower by two orders of magnitude than previous estimates, ultraviolet astrophysics below 912 A might not be anymore an unreachable goal