Pluto had its classification changed in 2006, from planet to “dwarf planet”. This change had great impact in the media. Pluto returned to the news due to the arrival of New Horizons probe to Pluto in July 2015. Whereas the understanding of the complexity involved in the definition of celestial bodies could help us to show science as a historic, social, collective, non-linear and non-neutral process, it is presented a historical survey of the episodes involving the various definitions for planet, since the first observations of the sky made by our ancestors until the resolutions that defined which are the attributes of a "planet " made at the 26th General Assembly of the International Astronomical Union, meeting at which it was decided to reclassify Pluto. In order contribute to help perform discussions about the nature of science involving Astronomy themes, it is explained which features of scientific knowledge become evident during the study of the mentioned episodes.