was a Japanese

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

, best known for his discovery that many

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

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.

Biography

Hirayama studied astronomy at

Imperial University of Tokyo , abbreviated as or UTokyo, is a public research university located in Bunkyō, Tokyo, Japan. Established in 1877, the university was the first Imperial University and is currently a Top Type university of the Top Global University Project by ...

and graduated in 1897. He taught astronomy in the engineering school of the General Staff Office of the Japanese Army between 1897 and 1901. In 1906 he became Assistant Professor of Astronomy at Tokyo Imperial University; in 1919 he became a Professor. From 1906 to 1907 Hirayama was a member of the Committee that determined the latitude border at

Sakhalin Sakhalin ( rus, Сахали́н, r=Sakhalín, p=səxɐˈlʲin; ja, 樺太 ''Karafuto''; zh, c=, p=Kùyèdǎo, s=库页岛, t=庫頁島; Manchu: ᠰᠠᡥᠠᠯᡳᠶᠠᠨ, ''Sahaliyan''; Orok: Бугата на̄, ''Bugata nā''; Nivkh ...

after the

Russo–Japanese War The Russo-Japanese War ( ja, 日露戦争, Nichiro sensō, Japanese-Russian War; russian: Ру́сско-япóнская войнá, Rússko-yapónskaya voyná) was fought between the Empire of Japan and the Russian Empire during 1904 and 1 ...

. In 1911 he received a doctoral degree "with several papers about latitude variation". Hirayama started working on asteroids in 1905; in 1918 he published papers "Researches on the distribution of the mean motions of the asteroids" and "Groups of asteroids probably of common origin", and, later "Families of asteroids" (1922) and "Note on an explanation of the gaps of the asteroidal orbits" (1928). In 1935 he published his main work, ''Asteroid''. The crater Hirayama on the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

is jointly named after him and

Shin Hirayama was the first Japanese astronomer to discover an asteroid. In 1900 he discovered 498 Tokio and 727 Nipponia. The crater Hirayama on the Moon is jointly named after him and Kiyotsugu Hirayama was a Japanese astronomer, best known for his ...

. The asteroid

1999 Hirayama 1999 Hirayama ( ''prov. designation'': ) is a dark background asteroid from the outer region of the asteroid belt, approximately in diameter. It was discovered on 27 February 1973, by Czech astronomer Luboš Kohoutek at the Hamburger Bergedorf ...

is named in his honour.

References

External links

月の命名

''Groups of asteroids probably of common origin'', Astronomical Journal, Vol. 31, No. 743, pp. 185-188
October 1918 *
Obituary Notices
(

Monthly Notices of the Royal Astronomical Society ''Monthly Notices of the Royal Astronomical Society'' (MNRAS) is a peer-reviewed scientific journal covering research in astronomy and astrophysics. It has been in continuous existence since 1827 and publishes letters and papers reporting orig ...

, Vol. 107, p. 42-44 - Obituary Notices :- Hirayama, Kiyotsugu) 1874 births 1943 deaths 20th-century Japanese astronomers People from Sendai 19th-century Japanese astronomers {{japan-astronomer-stub