He was born in Kyoto, the eldest son of Yasui Santetsu, a go master serving the shogunate. The Yasui were one of the houses that played castle go before the shogun. Though born into a go family, Harumi would make his name in the study of stars and calendars.
His father died, and while still a boy he succeeded as the second Yasui Santetsu. While training as head of a go house, he grew deeply interested in mathematics, astronomy and calendar science, learning mathematics and astronomy from Ikeda Masaoki and Okanoi Gentei and developing his talent.
He played castle go at Edo Castle for the first time and won. Around the same time he began observations to measure the latitude of various places, deepening his interest in astronomy. He later studied Shinto and Confucianism with Yamazaki Ansai and onmyodo with Tsuchimikado Yasutomi, drawing on many fields for his calendar studies.
In castle go he played Hon'inbo Dosaku, hailed as a master, and tried the bold opening of placing his first stone on tengen, the center point of the board. He lost by nine points, but the game is remembered as showing Harumi's willingness to try new ideas even in go.
The Senmyo calendar then in use had been made in Tang China and used for over 800 years, and had drifted about two days from the real motions of the heavens. Harumi petitioned the shogunate for a new calendar based on the Yuan Shoushi calendar, with the backing of Hoshina Masayuki, lord of Aizu.
To promote reform he offered an eclipse prediction based on the Shoushi calendar, but it proved wrong. It was a bitter setback, but he rethought the cause and is said to have realized that because China and Japan lie at different longitudes, a Chinese calendar could not be used unchanged.
The calendar he had reworked through repeated observation to fit Japan's position was approved, to be used from the next year as the Jokyo calendar, the first made by a Japanese. For this he was appointed the first official of the shogunate's new post of tenmonkata, the office of astronomy.
As tenmonkata he moved to Edo. Calendars had been made under the imperial court in Kyoto, but with the new office the center of calendar making shifted to the shogunate. In Edo Harumi continued observing and worked to improve the calendar's accuracy.
He was given a residence and observatory at Honjo and carried out full-scale astronomical observation. The next year he made celestial and terrestrial globes, showing the positions of the stars and the shape of the earth in visible form. A celestial globe he made survives and is an Important Cultural Property.
Based on his observations he compiled the star chart Tenmon Seisho, adding stars seen in Japan to the Chinese constellations. He is said to have added several dozen new constellations to the traditional Chinese ones, the fruit of his effort to observe Japan's sky with Japanese eyes.
Around this time he changed his surname to Shibukawa, said to be an ancestral name. It is thought to have meant founding a new house of astronomers separate from the Yasui go family, and the post of tenmonkata was handed down in the Shibukawa family for generations.
This year his son Hirotada, his intended heir, died suddenly, and Harumi died in Edo soon after, as if following him. The Jokyo calendar was used for about 70 years, and the office of tenmonkata, carried on by Takahashi Yoshitoki, teacher of Ino Tadataka, and others, supported the growth of Japanese astronomy.
Sakai TadakiyoItō JinsaiTokugawa MitsukuniKaibara EkikenKeichūTokugawa IetsunaIhara SaikakuSeki Takakazu
People of the Edo period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.