Dr. Yoshihide Kozai, the last Director General of the Tokyo Astronomical Observatory (TAO), and the founding Director General of its successor, the National Astronomical Observatory of Japan (NAOJ), and former President of the International Astronomical Union (IAU) died at the age of 89 in Tokyo on 5 February 2018. His specialty was celestial mechanics applied to satellites — natural or artificial — and he was a member of the Division on Dynamical Astronomy (DDA) of the American Astronomical Society (AAS).
Dr. Kozai’s early career coincided with the exciting era of space exploration when it was literally taking off. One of his prominent works conducted during his stay in the United States from 1958 to 1963 is included in the AAS’s centennial Issue, a special edition of the Astrophysical Journal published in 1999. He enabled the precise forecast of the orbital motion of artificial satellites around the Earth. The current generation might be familiar with the Kozai mechanism (often called the Kozai-Lidov mechanism), which can explain the migration of giant planets into the proximity of their host stars. Its original application was for the moons of Saturn, and it is applicable to exoplanetary systems.
After his return to Japan, Dr. Kozai promoted celestial mechanics research at TAO while he was affiliated with the University of Tokyo. Later he became the Director General in 1981 and led the conversion of TAO to a national institution integrating other institutions. He continued as the first Director General of NAOJ until 1994. Faced with the daunting task of promoting world-class research at NAOJ and in Japan, he established or initiated advanced observational facilities (for example, the Subaru Telescope and Atacama Large Millimeter/submillimeter Array, or ALMA) and high-performance computing facilities. The current Director General of NAOJ, Dr. Masahiko Hayashi, says, “Dr. Kozai wanted his fellow astronomers in Japan to engage and solve the fundamental problems of the universe by utilizing these facilities. We — the current generation — owe much to him.”
Dr. Kozai’s work was not confined in Japan. He served as President of the IAU from 1988 to 1991 and was the first Japanese to take that position. For his long years of research and education, the AAS DDA honored him with its Brouwer Award in 1990.
His fellow astronomers and astronomy educators celebrated his 90th birthday only two months ago, according to the traditional Japanese account of a person’s age. As he was always, his curious mind went beyond his boldest students’ imaginations, asking the participants many questions. One could see his influence in many areas, inside and outside of academia.
It made no difference to him whether one is at a university or not, or whether a person is in Japan or abroad. After all, the sky is one and we know only one universe to cherish. Dr. Kazunari Shibata, the current president of the Astronomical Society of Japan (ASJ), says, “Dr. Kozai was the president of ASJ between 1983 and 1985. The community mourns this tremendous loss of a shining star from this world. The only encouraging thought is that his legacy is well alive amongst the hearts of many.”
