In much the same way as a real observatory consists of a collection of unique instruments, the VO consists of a collection of data centres each with unique collections of observational data, software systems and processing capabilities.
The main goal is to allow transparent and distributed access to data available worldwide. This allows scientists to discover, access, analyze, and combine observational and laboratory data from heterogeneous data collections in a user-friendly manner.
The IVOA (International Virtual Observatory Alliance) is a standards body created by astronomical VO projects to develop and formalize the interoperability standards upon which the VO implementations are constructed.
Virtual Solar Terrestrial Observatory: Tetherless World Research Constellation at Rensselaer Polytechnic Institute in conjunction with the High Altitude Observatory of National Center for Atmospheric Research
TELEIOS: European Union-funded virtual observatory for Earth observation data. Powered by the CWIMonetDB scientific database, it provides access to TerraSAR-X archive of the DLR.