The Temple of Apollo in Didyma: An Oracle with a Celestial Bearing

The Temple of Apollo in Didyma, located on the Aegean coast of southwestern Turkey, is not aligned towards the cardinal directions: GPS measurements and satellite imagery indicate that the azimuth of the temple is 55.117°. Lack of prominent geological features in the surrounding landscape raise the idea of a probable celestial orientation. Various orientation studies have suggested bright stars of Gemini, sunrise direction during the summer solstice or the heliacal rising direction of Cygnus and Lyra during the winter solstice as potential vantage directions, and we propose that the temple is aligned towards the heliacal rising direction of Castor (a Geminorum). During the Hellenistic period Castor’s heliacal rise also coincided with the summer solstice, and we believe this alignment serves calendrical and symbolic purposes. We rest our case on astronomical computations, classical texts, archaeological evidence and the unique architectural plan of the temple.