Katsuo Tanaka was born in 1943 in Tokyo to a prosperous family who encouraged him in the difficult preparation for Tokyo University. He completed undergraduate and graduate studies there, working on radiative transfer and line formation. He obtained his Ph.D degree in 1971 for study of chromospheric spectra from the 1966 eclipse in Peru, working under Prof. Z. Suemoto.
In 1970 Tanaka moved to the Tokyo Astronomical Observatory, shifting to studies of solar activity and flares. He spent 1971-3 in postgraduate studies at Caltech, beginning a long collaboration with Zirin and the Big Bear Solar Observatory. He conducted a landmark study of the great flares of August 1972 and also discovered the twinning or double structure of spicules, and, with A. Bhatnagar, made important measurements of Hα oscillations.
On his return to Tokyo, he played a critical role in the immensely successful Astro-A (renamed "Hinotori") satellite project, launched in 1981, which recorded more than 700 solar flares. Tanaka built a Bragg Crystal spectrometer which used the spin of the satellite to scan. the spectrum, detecting a superhot component (>3x107 °K) in solar flares, strong blue shifts in X-ray emission lines and the first evidence of Fe XXVI. His energetic leadership led to successful analysis of data from all the instruments.
Tanaka was invited to summarize his results in an article in Publications of Astronomical Society of Japan in 1987, the first invited review paper in this journal. He proposed a classification of X-ray flares into three types: type A or hot thermal flares, type B or impulsive flares, and type C or gradual hard flares. He was awarded the Inoue Science Foundation Prize in 1985 for his achievement in flare research.
Tanaka had a strong interest in ground-based observations, and began the development of a Solar Cycle Telescope Project, which still continues.
The Solar-A spacecraft (Yoh-Koh), which was successfully launched in August 1991, owed a great deal to Tanaka's enthusiasm as well as his success in the Hinotori project.
In 1983 Tanaka was found to have myelogenous leukemia, which he bravely fought for eight years, working to the very end. In his short life he published 48 papers in Ap.J., P.A.S.J., Solar Physics and other journals. Particularly important is the Hinotori Symposium, 1982.
Tanaka loved pop music, sci-fi movies, swimming, yoga, and so on. He was a talented artist, producing beautiful drawings for his papers. He was a tireless worker, at home with instruments, observations and theory. He had a great respect for tradition, not hesitating to use fortune-tellers and traditional Chinese medicine along with the most modern drugs. He was one of the first recipients of alpha interferon, which produced excellent results for some time, but finally proved insufficient.
On January I, 1990, Katsuo went to the seashore with his wife, Chisako, and two daughters, Kaoru and Sanae. The next day he passed away. He was a dynamic force in Japanese astronomy and an inspiration to all.