part of material entity astronomical body astronomical body part A material part of an astronomical body. Material parts of astronomical bodies generally have boundaries formed by discontinuities in qualities, composition, or other physical characterisitcs. These boundaries are sometimes sharp, and sometimes diffuse, with different classification systems and communities declaring varying thresholds (e.g. for where a shoreline, forest, or other entity begins and ends). However, some boundaries are declared by fiat - that is, by arbitrary human convention or decree - particularly by regulatory or other authorities and communities of practice. The classes in this hierarchy attempt to offer generalisable definitions that allow multiple classfiication systems to map to and interoperate through. If desired, we can create classes that declare thresholds used by a given authority or community under the more generic ones, annotated with source information. envoPolar envoAstro