Hirayama was born in Tokyo on 24 April 1934. His grandfather, Shin Hirayama, was the second Director General of Tokyo Astronomical Observatory (TAO) of the University of Tokyo. He graduated from the astronomy course of the Department of Physics, the University of Tokyo, in 1957 and proceeded to the graduate school. He was appointed as research assistant at TAO in 1961 while he was still in the graduate course. Later in 1964 he received a Doctor of Science degree from the University of Tokyo for his research on spectroscopic studies of prominences. He was promoted to associate professor in 1971, and to professor in 1982. He served as Vice Director General of NAOJ from its foundation in July 1988 to March 1992.
His theoretical flare model described in his 1974 paper (doi:10.1007/BF00153671) is one of the key papers of the so-called CSHKP (Carmichael-Sturrock-Hirayama-Kopp-Pneuman) model featuring magnetic reconnection as its fundamental mechanism. His paper has been cited more than 1000 times according to the ADS.
The spectroscopic study of prominences has been Hirayama’s life work, and he wrote a review article in the 100-th anniversary volume of Solar Physics in 1985 (doi:10.1007/BF00158439).
He was the principal investigator (PI) of the soft X-ray telescope (SXT) on board Yohkoh, which was launched in 1991. Together with Loren Acton (the US-side PI of SXT), Saku Tsuneta (the actual Japan-side central person), and Yohkoh project manager Yoshiaki Ogawara of ISAS, Hirayama led the team smoothly and achieved a very successful mission.
Much before the successful high-resolution observations with the optical telescope SOT of the Hinode satellite (launched in 2006), Hirayama started observations of granulation and faculae with balloon-borne telescopes in the 1970s, and derived the center-to-limb variations of the contrast of granules and facular bright points, with the highest accuracy at his time.
In March 1995 he retired from NAOJ and moved to Meisei University in the western suburbs of Tokyo, joining Eijiro Hiei (Hirayama’s senior colleague) who also moved from NAOJ in 1992. After he retired from Meisei Univesity in March 2004, he stayed at home but continued his research. A big loss to him was the death of his wife in 2015. In 2023 he moved to a nursing facility, and completed his memoir article in Solar Physics (doi:10.1007/s11207-025-02431-1), which was published in February 2025.
Near the midnight of March 5, 2025, he passed away peacefully, surrounded by his children. Tadashi Hirayama will be deeply missed by his family, collaborators, students, and friends all over the world. A more complete obituary will appear in Solar Physics
Takashi Sakurai