The quest for high resolution has preoccupied radio astronomers ever
since radio waves were first detected from space fifty years ago. This
venture was par- ticularly stimulated by the discovery of quasars, and
led to the development of interferometer techniques using baselines of
transglobal dimensions. These meth- ods have become known as Very Long
Baseline Interferometry (VLBI). Arrays of radio telescopes situated all
over the Earth (or even in space) are regularly used for researches in
radio astronomy, reaching resolutions as small as a fraction of a milli
arcsecond. The technique also allows the measurement of the positions of
the radio telescopes to a few millimeters and so VLBI has become a major
tool in geodesy and the study of the rotation of the Earth. VLBI has now
passed the pioneer stage and is becoming a standard facility available
to astronomers and geodesists, requiring the coordination of the
operations of indpendently owned radio telescopes around the world. In
Europe observatories from England, Federal Republic of Germany, France,
Italy, Poland, Sweden and The Netherlands are coordinated in their VLBI
activity by the European VLBI Network Consortium (EVN). The Programme
Committee of the EVN allocates time to scientific projects on a routine
basis three times a year. The Unites States has a similar arrangement of
a network of independent radio observatories, and joint experiments
using 'Global Network' are often made.
