IVOA Recommendation: Simple Cone Search Version 1.03
  This specification defines a simple query protocol for retrieving records from a catalog of astronomical sources. The query describes sky position and an angular distance, defining a cone on the sky. The response returns a list of astronomical sources from the catalog whose positions lie within the cone, formatted as a VOTable. This version of the specification is essentially a transcription of the original Cone Search specification in order to move it into the IVOA standardization process. 
Roy Williams, Robert Hanisch, Alex Szalay, Raymond Plante
astro-ph.IM