The Chandra and Hubble Telescopes are in space and each costs (through operations) several billion dollars. VLT is on the ground but over 20 years of operations will also cost in excess of a billion. They all fall therefore in the category of what I consider Big Science, and they have required new technology and management tools to be developed particularly with regard to data management.
I will highlight some of the major findings obtained with these observatories, some by a single facility, some in cooperative research programs. These findings are among the most unexpected and baffling results in astronomy. They include the study of intergalactic plasmas, of super massive black holes and of the properties of dark matter as well as the discovery of dark energy. We now believe that dark matter and dark energy constitute most of the matter in our universe. Since neither the nature of dark matter nor of dark energy is understood, astronomy is posing some of the most fundamental questions on the nature of the physical universe we live in.
I will briefly discuss how astronomy is carried out when confronted with the very large quantities of data produced by these telescopes and of the development of end to end data systems for data retrieval and archiving. The effects of these methodological changes have been profound for all astronomers and they have also changed the sociology of the field. Some concerns for the future exist regarding the concentration of technical expertise in a few groups building the facilities while the remainder of the community become consumers of data.
A separate but important development has been the exponential increase of high quality astronomical information shared with the general public, with as yet unknown effects.