was a Japanese physician and

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

who helped integrate western and Japanese astronomy in the

Edo period The , also known as the , is the period between 1600 or 1603 and 1868 in the history of Japan, when the country was under the rule of the Tokugawa shogunate and some 300 regional ''daimyo'', or feudal lords. Emerging from the chaos of the Sengok ...

. 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 is the third-largest island of Japan's Japanese archipelago, four main islands and the most southerly of the four largest islands (i.e. excluding Okinawa Island, Okinawa and the other Ryukyu Islands, Ryukyu (''Nansei'') Ryukyu Islands, Islands ...

. Asada spent much of his career in the flourishing commercial city of

Osaka is a Cities designated by government ordinance of Japan, designated city in the Kansai region of Honshu in Japan. It is the capital of and most populous city in Osaka Prefecture, and the List of cities in Japan, third-most populous city in J ...

, 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 The Society of Jesus (; abbreviation: S.J. or SJ), also known as the Jesuit Order or the Jesuits ( ; ), is a religious order (Catholic), religious order of clerics regular of pontifical right for men in the Catholic Church headquartered in Rom ...

missionaries in

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

. 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 in 1609 (except the third law, which was fully published in 1619), describe the orbits of planets around the Sun. These laws replaced circular orbits and epicycles in ...

. 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 Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

is named after him.

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Further reading