{{short description|Japanese celestial mechanician}} {{Use dmy dates|date=July 2021}} {{Infobox scientist | name = Yusuke Hagihara | image = Yusuke Hagihara 01.jpg | caption = Hagihara in 1954 | birth_date = 28 March 1897 | birth_place = Osaka, Japan | death_date = 29 January 1979 | death_place = Tokyo, Japan | fields = {{hlist|Astronomy|Celestial mechanics}} | workplaces = University of Tokyo <br/> Tokyo Astronomical Observatory <br/> Japan Academy | alma_mater = Tokyo Imperial University (BSc 1921) <br/> University of Tokyo (D.Sc. 1930) | notable_students = Yoshio Fujita }}

{{Nihongo|'''Yusuke Hagihara'''|萩原 雄祐|Hagihara Yūsuke|28 March 1897 in Osaka &ndash; 29 January 1979 in Tokyo}} was a Japanese astronomer noted for his contributions to celestial mechanics.<ref name="Herget1979" />

== Life and work ==

Hagihara graduated from Tokyo Imperial University with a degree in astronomy in 1921 and became an assistant professor of astronomy there two years later.<ref name="Kozai1979">{{cite journal | last = Kozai | first = Yoshihide | title = Yusuke Hagihara | journal = Quart. Jour. Royal Astron. Soc. |volume = 20 | issue = 3 | date = 1979 | pages = 325–8}}</ref> In 1923 the Japanese government sent him abroad as a traveling scholar. Hagihara went to Cambridge University in England to study differential equations under the mathematician Henry Frederick Baker<ref name="Kozai1979"/> and relativity alongside Paul Dirac under the astrophysicist Sir Arthur Stanley Eddington.<ref name="Herget1979" /><ref name="Kozai1998" /> He was a visiting scholar in France, Germany, and the United States.<ref name="Herget1979" />

He returned to Japan in 1925 but left for the United States three years later to study the topology of dynamical systems at Harvard University under George David Birkhoff on a Rockefeller Foundation Fellowship.<ref name="Kozai1998">{{cite journal | last = Kozai | first = Yoshihide | title = Development of Celestial Mechanics in Japan | journal = Planet. Space Sci. | volume = 46 | issue = 8 | date = 1998 | pages = 1031–36|bibcode = 1998P&SS...46.1031K | doi=10.1016/s0032-0633(98)00033-6}}</ref>

Hagihara finished his studies at Harvard in 1929 and returned again to the University of Tokyo, where, in 1930, he completed a D.Sc. dissertation on the stability of satellite systems.<ref name="Kozai1979"/> In 1935, he published a paper showing that the trajectory of a test particle in the Schwarzschild metric can be expressed in terms of elliptic functions.<ref name="Kozai1998" /> For more than a decade after 1937, he investigated the distribution of electron velocities in planetary nebulae.<ref name="Kozai1998" />

He was promoted to full professor at the University of Tokyo in 1935.<ref name="Kozai1979" /> From 1945 to 1957 he was the director of the Tokyo Astronomical Observatory and subsequently was a professor at Tohoku University (1957–1960) and president of Utsunomiya University (1961–1967).<ref name="Kozai1998" /> In 1961 he was elected vice-president of the International Astronomical Union and president of the IAU's commission on celestial mechanics.<ref name="Kozai1979" />

He retired from all of his official duties, except for the Japan Academy, in 1967 and devoted himself to writing his comprehensive five volume work, ''Celestial Mechanics'', which was based on his lecture notes.<ref name="Kozai1979"/>

Hagihara was regarded as a quiet and cultured gentleman, an excellent teacher and a capable administrator.<ref name="Herget1979">{{cite journal|last=Herget|first=Paul|authorlink=Paul Herget|date=1979|title=Yusuke Hagihara|url=http://www.physicstoday.org/resource/1/phtoad/v32/i6/p71_s1?bypassSSO=1|journal=Physics Today|volume=32|issue=6|pages=71|bibcode=1979PhT....32f..71H|doi=10.1063/1.2995600|doi-access=free}}</ref><ref name="Kozai1979"/>

He has pointed out the importance of the post-Newton models for celestial mechanics, namely that developed by Georgi Manev.{{citation needed|date=May 2014}}

== Honors == * The main-belt asteroid 1971 Hagihara was named in his honor.<ref name="springer" /> * Fellow of the Royal Astronomical Society * Chairman of the National Committee of Astronomy (Japan) * Member Japan Academy * Member Science Council of Japan * Order of Cultural Merit (Japan) * Recipient of the James Craig Watson Medal from the U.S. National Academy of Science (1960)

== Works == * {{cite book | last = Hagihara | first = Yusuke | title = Celestial mechanics : Dynamical principles and transformation theory (vol. 1) | place = Cambridge | publisher = MIT Press | year = 1970 | isbn=978-0-262-08037-8}} * {{cite book | last = Hagihara | first = Yusuke | title = Celestial mechanics: Perturbation theory (vol. 2, parts 1 and 2)| place = Cambridge | publisher = MIT Press | year = 1972}} * {{cite book | last = Hagihara | first = Yusuke | title = Celestial mechanics: Differential equations in celestial mechanics (vol. 3, parts 1 and 2) | place = Tokyo | publisher = Japan Society For the Promotion of Science | year = 1975}} * {{cite book | last = Hagihara | first = Yusuke | title = Celestial mechanics: Periodic and quasi-periodic solutions (vol. 4, parts 1 and 2) | place = Tokyo | publisher = Japan Society For the Promotion of Science | year = 1976}} * {{cite book | last = Hagihara | first = Yusuke | title = Celestial mechanics: Topology of the three-body problem (vol. 5, parts 1 and 2) | place = Tokyo | publisher = Japan Society For the Promotion of Science | year = 1977}} * {{cite book | last = Hagihara | first = Yusuke | title = Theories of equilibrium figures of a rotating homogeneous fluid mass | location = Washington, D.C. | publisher = U. S. Government Printing Office | date = 1971 | id = NAS 1.21:186}}

== See also == {{Portal|Biography|Physics}} * Schwarzschild geodesics * List of contributors to general relativity {{clear}}

== References == {{reflist|30em|refs=

<ref name="springer">{{cite book |title = Dictionary of Minor Planet Names – (1971) Hagihara |last = Schmadel | first = Lutz D. |publisher = Springer Berlin Heidelberg |page = 159 |date = 2007 |isbn = 978-3-540-00238-3 |doi = 10.1007/978-3-540-29925-7_1972 |chapter = (1971) Hagihara }}</ref>

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{{refbegin}} * {{cite book | editor-last = Greene | editor-first = Jay E. | title = McGraw-Hill Modern Scientists and Engineers. 3 vols | location = New York | publisher = McGraw-Hill | date = 1980}} {{refend}}

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{{DEFAULTSORT:Hagihara, Yusuke}} Category:1897 births Category:1979 deaths Category:University of Paris alumni Category:Harvard University alumni Category:Academic staff of the University of Tokyo Category:Recipients of the Order of Culture Category:Recipients of the Order of the Sacred Treasure, 1st class Category:20th-century Japanese astronomers Category:People from Osaka Category:Scientists from Osaka Category:Academic staff of Tohoku University Category:University of Tokyo alumni