Kepler - Johannes Kepler

German astronomer. Born as the eldest son of a tavern owner in Weyl, Duchy of Württemberg, he was sickly all his life. At the age of four, he lost his eyesight due to smallpox, and at the age of 17, his father died of a war injury, so he supported his family from then on. Despite being plagued by illness, poverty, and social unrest such as the religious wars of the time, he pursued the true nature of planetary motion and discovered the so-called "Kepler's Laws."

In the year his father died, he was accepted as a scholarship student at the Department of Theology at the University of Tübingen, hoping to become a priest. During his liberal arts course, he was particularly interested in the astronomy lectures of Professor Michael Mästlin (1550-1631), and his view of nature was opened to the Copernican theory of the universe. During his specialist course, he was also drawn to Neoplatonism. It is this influence that has led to the mixture of modern scientific theory and medieval mystical thought in his writings.

After graduating from university in 1594, he was appointed as a mathematics teacher at the Graz High School. At the same time, he attempted to compile an astrological calendar at the request of the mayor, and his predictions of severe winters and wars in society were well received. During this time, he developed ideas about the structure of the universe, and in 1596, he published his first book, Mysterium cosmographicum . This was a semi-speculative concept in which the six planets (Mercury, Venus, Earth, Mars, Jupiter, and Saturn) were centered around the sun and were circumscribed and inscribed in five regular polyhedrons, maintaining their distance from each other. Through this work, he became acquainted with Tycho Brahe and Galileo. The following year, in 1597, he married, but persecution of Protestants began in 1599, and he moved to Prague in 1600. Tycho Brahe, who had fled from Copenhagen, continued to observe the movement of Mars under the protection of Rudolf II. Kepler was granted royal permission to become Tycho's assistant, and they collaborated for a year and a half until Tycho's death. At the time of his mentor's death, Kepler was entrusted in his will with organizing the observational data he had accumulated over the past 16 years. At the same time, he was appointed his successor as court mathematician. This transfer of research from the foremost observer of the time to theorist was an important turning point for the development of the heliocentric theory.

Kepler's further efforts bore fruit in the 1609 work Astronomia nova , which included the first and second laws of Kepler's Laws. The first law, "The planets orbit in ellipses with the Sun as one focus," was discovered because the orbit of Mars was quite elliptical, while the orbit of the Earth was almost circular. The second law, "The radius between a planet and the Sun sweeps out the same area in the same time," was a correct conclusion, despite some misunderstandings in the thought process. That is, Kepler derived the second law from the following points: "The driving force behind the revolution of the planets is the magnetic force of the Sun," "Therefore, the planets are propelled by the rotation of the Sun," "The propulsive force is inversely proportional to the distance to the center of the sun," and "The sum of the radii of movement is the area of ​​a sector." These were based mainly on Tycho's Mars observation data.

The third law, "The cube of the semi-major axis of the planetary orbit (the average distance between the sun and the planet) is proportional to the square of the orbital period," was of such quality that it took another 10 years to discover it, as it could only be found by examining the data of all the planets. It was included in Harmonice mundi (Harmony of the World) in 1619. He carefully examined simple proportional relationships among a large number of numerical values ​​and discovered the correspondence between the orbital period and the average distance, and reminisced that "my long-held wish since the beginning of my astronomy career has been fulfilled." However, the rest of the book seeks harmony as the basic spirit of the universe, and emphasizes the principles of planetary motion, especially by analogy with the principles of harmony. Although this mystical thinking is akin to empty theory, his predictions of planetary positions calculated logarithmically based on the three laws were published under the name of Rudolph's Tables (1626), and became the basis of nautical almanacs for long-distance voyages.

In addition to the above works, Kepler also produced many other works, including De Nova (1606), De Refraction (1611), New Measurements of the Wine Barrel (1615), De Comtes (1618), Outlines of Copernican Astronomy (1621), The Theory of Logarithms (1624), and Dreams of Lunar Astronomy (posthumous manuscript). However, he did not enjoy a happy family life, losing his wife and one child to smallpox in 1611, and working hard to secure the release of his elderly mother who was accused of witchcraft. He changed his workplace and address several times, and eventually died in the street in the snow after going to petition Prince Wallenstein for unpaid wages.

[Shimamura Fukutaro]

"Complete Works of the World's Greatest Thoughts 31: Galileo Kepler, edited and translated by Yabuuchi Kiyoshi and Shimamura Fukutaro (1963, Kawade Shobo Shinsha)" ▽ "Kepler's Dream, by J. Kepler, translated by Watanabe Masao and Enomoto Emiko (1972, Kodansha/Kodansha Academic Library)" ▽ "The Mysteries of the Universe, translated by Otsuki Shinichiro and Kishimoto Yoshihiko (1982/New Edition, 2009, Kousakusha)" ▽ "The Harmony of the Universe - A Timeless Cosmology, translated by Kishimoto Yoshihiko (2009, Kousakusha)" ▽ "Johannes Kepler, by A. Koestler, translated by Oobi Shinya and Kimura Hiroshi (1971, Kawade Shobo Shinsha/Chikuma Gakugei Bunko)"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

ドイツの天文学者。ウュルテンベルク公領ワイルの居酒屋の長男として生まれ、終生、病弱であった。4歳で天然痘のため視力を弱め、17歳のとき父が戦傷死し、以来、家族を扶養した。病身、貧困に加えて当時の宗教戦争といった社会不安にさいなまれながら、惑星運動の実相を追究し、いわゆる「ケプラーの法則」を発見した。

　父が死去した年、聖職者を志してチュービンゲン大学の神学科給費生に合格、教養課程で、とくに教授メストリンMichael Mästlin（1550―1631）の天文学講義に興味をもち、コペルニクスの宇宙体系の説話に自然観を開眼した。また、専門課程の修得では新プラトン主義に傾倒した。彼の著述のなかに近代的な科学理論と中世的な神秘思想とが混在しているのは、この影響である。

　1594年大学卒業後、グラーツ高等学校の数学教師に赴任、かたわら市長の委託で占星暦の編修を試み、厳冬や戦乱などの世相予言が的中して評判となった。その間、宇宙構造に関する構想をめぐらせて、1596年、最初の著作『宇宙の神秘』Mysterium cosmographicumを刊行した。これは、太陽を中心として6惑星（水星・金星・地球・火星・木星・土星）が、5個の正多面体に順次外接・内接することによって、その距離が保たれるという半思弁的な設定であった。この著述によって、ティコ・ブラーエやガリレイの知己を得た。翌1597年結婚したが、1599年に新教徒への迫害が始まり、1600年プラハへ移住した。ここにはコペンハーゲンから亡命したティコ・ブラーエがルードルフ2世の保護の下で火星の運行の観測を続行していた。ケプラーは勅許を得てティコの助手となり、以来ティコ他界までの1年半の間、共同研究を行った。恩師の臨終に際して、16年間にわたる観測資料の整理を遺言委託された。同時に後継者として宮廷数学官に任じられた。この当代随一の観測家から理論家への研究の引き継ぎは地動説の発展にとっては重要な契機となった。

　その後のケプラーの精進は1609年の『新天文学』Astronomia novaとなって結実し、ここにいわゆる「ケプラーの法則」の第一、第二法則を収めた。第一法則「惑星は太陽を一焦点とする楕円(だえん)軌道を描く」の発見は、地球の軌道がほとんど円形に近いのに対して、火星の軌道がかなり楕円であったことから導き出された。第二法則「惑星と太陽を結ぶ動径は同一時間に等しい面積を掃く」は、思考の過程においていくつかの思い違いもあったが、正しい結論に達した。すなわち、ケプラーは、「惑星公転の原動力は太陽の磁気力による」「したがって太陽の自転によって惑星は推進する」「推進作用は日心距離に反比例する」「移動半径の総和が扇形面積となる」として第二法則を導いたのである。これらは、もっぱらティコの火星観測資料に基づくものであった。

　第三法則「惑星軌道の長半径（太陽―惑星間の平均距離）の3乗は公転周期の2乗に比例する」は、全惑星の資料を見渡さなければ得られない質のものであり、その発見にはさらに10年間を要した。1619年の『世界の調和』Harmonice mundi（邦訳『宇宙の調和』）にそれが収録されている。多数の数値群のなかから単純比例関係を丹念に調べて、公転周期と平均距離との対応関係を発見したのであり、「天文を志した当初からの年来の望みが達せられた」と述懐している。とはいえ、この書の他の部分は、宇宙の基調精神を調和に求め、とくに和声学の原則との類推において惑星運行の原理を力説している。この神秘的思考は空論に類するが、3法則に基づいて対数計算した惑星の位置予報は『ルドルフ表』（1626）の名で刊行され、遠洋航海に必要な航海暦の基となった。

　以上の著書のほか、『新星論』（1606）、『屈折光学』（1611）、『葡萄酒樽(ぶどうしゅだる)の新計量』（1615）、『彗星(すいせい)論』（1618）、『コペルニクス天文学概要』（1621）、『対数の理論』（1624）、『月天文学の夢』（遺稿）など、多くの業績を残したケプラーであるが、家庭生活には恵まれず、1611年に天然痘で妻と1子を失い、魔女嫌疑の老母の放免に奔走しなければならなかった。職場と住所も幾度かかわり、最後はワレンシュタイン侯のもとに未払いの俸給の請願に赴き、雪中、路上で死去した。

［島村福太郎］

『藪内清・島村福太郎編・訳『世界大思想全集31　ガリレオ・ケプラー編』（1963・河出書房新社）』▽『J・ケプラー著、渡辺正雄・榎本恵美子訳『ケプラーの夢』（1972・講談社／講談社学術文庫）』▽『大槻真一郎・岸本良彦訳『宇宙の神秘』（1982／新装版・2009・工作舎）』▽『岸本良彦訳『宇宙の調和――不朽のコスモロジー』（2009・工作舎）』▽『A・ケストラー著、小尾信彌・木村博訳『ヨハネス・ケプラー』（1971・河出書房新社／ちくま学芸文庫）』

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