Issued by Greece (ΕΛΛΑΣ) in 1966, this 2.50-drachma commemorative stamp honors Hipparchus, the ancient Greek astronomer famed for founding trigonometry and creating the first comprehensive star catalog. The stamp was released for the inauguration of the Athens Planetarium, highlighted in the inscription at the top. The left vignette shows a classical profile of Hipparchus with a star symbol, while the right features an armillary sphere, symbolizing early astronomical observation. Printed in a refined green and black engraving style, this issue appeals strongly to collectors of science, astronomy, and Greek heritage themes.