Ptolemy is a proper noun referring to the ancient Greco-Egyptian astronomer and mathematician who authored influential geocentric models. In usage, it denotes his name as a figure, place-based surname in scholarly contexts, or as a reference in history of astronomy. The pronunciation is not intuitive from its spelling and is widely taught as /ˈtɒlɪmi/ or /ˈtoʊlɪmi/ depending on accent, with stress on the first syllable.
Full pronunciation guide
