Resolution B5, Definition of a Planet in the Solar System, 26th General Assembly

This is the International Astronomical Union's own Resolution B5, adopted by vote at its 26th General Assembly on 24 August 2006, the primary legal text that defined planet for the first time and reclassified Pluto and Ceres as dwarf planets. As the issuing body's own resolution it is the correct source for the fact, wording and date of that reclassification. Its limit is that it is a definitional and procedural document recording what was adopted, not an argument defending the definition against the substantial dissent it drew from planetary scientists at the time and since, so a claim about whether the definition is scientifically well founded needs a source engaging that ongoing debate rather than the resolution's own text.