was a Japanese physician and

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

who helped integrate western and Japanese astronomy in the

Edo period The or is the period between 1603 and 1867 in the history of Japan, when Japan was under the rule of the Tokugawa shogunate and the country's 300 regional '' daimyo''. Emerging from the chaos of the Sengoku period, the Edo period was characte ...

. He introduced several western astronomical instruments and methods into Japan and independently confirmed Kepler's third law. Asada was the pseudonym based on the name of his village. Born (birthday given as 6 February 1734, Japanese year Kyoho) as Yasuakira Ayabe, his father, Keisai Ayabe came from a landed Kitsuki clan from Bungo, Kyushu. Asada spent much of his career in the flourishing commercial city of

Osaka is a designated city in the Kansai region of Honshu in Japan. It is the capital of and most populous city in Osaka Prefecture, and the third most populous city in Japan, following Special wards of Tokyo and Yokohama. With a population of ...

, where he practiced medicine for a living. He, then, took over his father's practice as an official physician in 1767. Because of the Japanese government's policy of seclusion, Western scientific theory was generally available only through obsolete Chinese works edited by Jesuit missionaries in China. Yet Asada managed to construct sophisticated mathematical models of celestial movements and is sometimes credited with the independent discovery of

Kepler's third law In astronomy, Kepler's laws of planetary motion, published by Johannes Kepler between 1609 and 1619, describe the orbits of planets around the Sun. The laws modified the heliocentric theory of Nicolaus Copernicus, replacing its circular orbi ...

. Asada also studied anatomy in western texts and his learnings were incorporated into a compilation by his friend Riken Nakai (1732-1817) in ''Esso-rohitsu'' (1773). The crater Asada on the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

is named after him.

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