is a Japanese amateur astronomer and discoverer of minor planets and comets, born in KÃ Âchi, Japan.
Tsutomu Seki is the Director of the Geisei Observatory in KÃ Âchi, and in charge of the Comet Section of the Oriental Astronomical Association. Between 1961 and 1970, he had visually discovered six comets, including C/1965 S1 (Ikeya-Seki), the well known great comet of 1965.
He has also discovered a large number of asteroids such as 13553 Masaakikoyama and 5209 Oloosson, a near-Earth Amor asteroid and a Jupiter trojan, respectively. Many of his discoveries are named after famous sites in Kà Âchi, such as Harimaya-bashi, Ryà Âma (after Sakamoto Ryà Âma), Katsurahama beach, and Kagami-gawa.
Asteroid 3426 Seki, discovered by Karl Reinmuth at the Heidelberg Observatory in 1932, was named in his honor. The official naming citation was published by the Minor Planet Center on 16 December 1986 ().