The National Virtual Observatory's Sky Statistics Service allows astronomers to get a fast inventory of astronomical objects from various catalogs. These catalogs can be wavelength-based (x-ray sources, radio sources, etc.), phenomena-based (supernova remnants, planetary nebulae, variable stars, quasars, etc.), or may simply show where a telescope has been pointed. The Sky Statistics Service also allows astronomers to easily determine regions of overlap between catalogs. These images show the distribution of objects in a sample of the many astronomical catalogs that are accessible through the National Virtual Observatory.
Credit: National Virtual Observatory and California Institute of Technology (http://us-vo.org/)