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Kiyotsugu Hirayama (平山 清次, Hirayama Kiyotsugu, October 13, 1874 – April 8, 1943) was a Japanese astronomer, best known for his discovery that many asteroid orbits were more similar to one another than chance would allow, leading to the concept of asteroid families, now called "Hirayama families" in his honour.
- 月の命名 (in Japanese)
- Groups of asteroids probably of common origin, Astronomical Journal, Vol. 31, No. 743, pp. 185-188, October 1918
- (in English) Obituary Notices (Monthly Notices of the Royal Astronomical Society, Vol. 107, p. 42-44 - Obituary Notices :- Hirayama, Kiyotsugu)