Hiroki Kosai (香西 洋樹) is a Japanese astronomer with the Kiso Observatory. He is best known for helping to popularize astronomy in Japan and for his observations of comets and asteroids, most notably with his co-discovery the comet 1976 XVI. He is credited by the Minor Planet Center (MPC) with the discovery of nearly 100 asteroids.

Awards and honors

Asteroid 3370 Kohsai, discovered by Karl Reinmuth at Heidelberg Observatory in 1930, is named in his honor. The official naming citation was published by the MPC on 14 April 1987 (M.P.C. 11750).

List of discovered minor planets

Hiroki Kosai discovered several asteroids, all in collaboration with Kiichirō Furukawa and Goro Sasaki: