Bithynia. Nicaea. Severus Alexander (222-235). Ae 24 mm. 6.6 gm. Obv: M AVP CEV AΛEΞANΔPOC AV. Laureate, draped and cuirassed bust right. Rev: NIKAIEΩN IΠΠAPXOC. Hipparchus the astronomer seated on basis left, wearing himation over lower limbs; to left, globe on small column. RPC online 3183. Very Rare. Hipparchus the Astronomer is depicted on very few rare issues from Nicaea. Born c. 190 BC, his importance to classical astronomy is very significant. He is credited with compiling the first star chart, calculating the sizes of the sun and the moon, the length of the seasons, and applying a trigonometry table before any other mathematician.