What is the Virtual Observatory?
Astronomy has entered a new, data-rich era which needs new tools to exploit its riches. The Virtual Observatory (VO) is the generic name for the effort led by the world's major astronomical data centers to provide a seamless common interface to all public data. This effort includes a lot of software-standards work, invisible to the average astronomer, to make the archives work together smoothly, as well as public portals for astronomers to explore the data ocean - crossmatching catalogs, locating relevant images and spectra, performing preliminary analyses, and downloading the actual data for further analysis offline.

The global VO will link the archival data sets of space and ground-based observatories, catalogs of multi-wavelength surveys, and on-line distributed computational resources. At present the VO focusses mainly on extrasolar astronomy, although similar efforts have been explored in solar physics and solar system research.

 VO Organizations The CfA is involved in a number of VO-related organizations:

• The International Virtual Observatory Alliance (IVOA). The IVOA is an informal alliance of world VO efforts, and meets every six months at the Interoperability Meetings to define the VO standards. The IVOA has no budget of its own, and is just an aggregation of the separate national projects.
• The National Virtual Observatory (NVO) is the US-based prototype project, and was funded by NSF. It is being replaced in 2009 with the VAO:
• The US Virtual Astronomical Observatory (VAO) is the new (2009) US operational VO project, funded by NSF and NASA.

 How is the CfA involved?
With National Science Foundation (NSF) funding, the CfA is collaborating with the National (VAO) and International (IVOA) Virtual Observatory (VO) activities. Our current focus is the design of the software that will allow scientists and the public to access all the participant astronomy archives and retrieve and analyze data simply. This software will be based on a general description of all the astronomy data, which we call the Data Model. We expect also to coordinate the connection of the various CfA data archives to the VO and act as a center of expertise within the CfA on VO-related matters.