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A Report on Johannes Kepler W/laws

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Johannes Kepler

The Harmonies of the World

"By the study of the orbit of Mars, we must either arrive at the secrets of astronomy or forever remain in ignorance of them."

Johannes Kepler


Kepler, Johannes (1571-1630) who was a German astronomer and natural philosopher is noted for coming up with and verifying the three laws of planetary motion. These laws are now known as Kepler's laws of Planetary Motion. Johanne was born on December 27, 1571.


Johanne was born in Weil der Stadt in Swabia and moved to nearby Leonberg with his parents in 1576. His father was a mercenary soldier and his mother was the daughter of an innkeeper. He was their first child. His father left home for the last time when Johannes was five, and is believed to have died in a war in the Netherlands. Whenever he was a child, Kepler lived with his mother in his grandfather's inn. Sources said that he used to help by serving in the inn. Customers were amused by the child's unusual competence at math. Kepler's early education was in a local school and then at a nearby seminary, from which, intending to be ordained, he went on to enroll at the University of TÑŒbingen, a bastion of Lutheran orthodoxy.

Johannes Kepler

Leaving Prague for Linz

Johanne's years in Prague were peaceful, and scientifically productive. In fact, even when things went badly, he never seemed to have allowed external circumstances to prevent him from getting on with his work.

Things began to go very badly in late 1611. His seven year old son died. Kepler wrote to a friend that this death was particularly hard because the child reminded him so much of himself at that age. Then his wife died. Emperor Rudolf, whose health was failing, was forced to abdicate in favor of his brother Matthias, who, like Rudolf, was a Catholic but (unlike Rudolf) did not believe in tolerance of Protestants. Kepler had to leave Prague. Before he departed he had his wife's body moved into the son's grave, and wrote a Latin epitaph for them. He and his remaining children moved to Linz (now in Austria).

Marriage and Wine Barrels

Johanne seemed to have married his first wife, Barbara, for love (though the marriage was arranged through a broker). The second marriage, in 1613, was a matter of practical necessity. He needed someone to look after the children. Kepler's new wife, Susanna, had a "crash course" in Kepler's character. A dedicatory letter to the resultant book explains that at the wedding celebrations he noticed that the barrels of wine barrels were estimated by means of a rod slipped in diagonally through a hole, and he began to wonder how that could work.

The result was a study of the volumes of solids of revolution (New Stereometry of wine barrels, Nova stereometria doliorum, Linz, 1615) in which Kepler, basing himself on the work of Archimedes, used a resolution into 'indivisibles'. This method was later developed by Bonaventura Cavalieri (c. 1598 - 1547) and is part of the ancestry of the infinitesima.

Development of Laws

He was influenced by a mathematics professor, Michael Maestlin, an advocate of the heliocentric theory of planetary motion first developed by Nicolaus Copernicus. Kepler accepted the Copernican Theory immediately. He believed that the simplicity of Copernican planetary ordering must have been God's plan.

In 1594, when Kepler left TÑŒbingen for Graz, Austria, he worked out a complex geometric hypothesis to account for distances between the planetary orbits. Orbits that he mistakenly assumed were circular. (Kepler later found that planetary orbits are elliptic; nevertheless, these preliminary calculations agreed with observations to within 5 percent.) Kepler then proposed that the sun emits a force that diminishes inversely with distance and forces the planets around in their orbits. Kepler published his account in a treatise entitled Mysterium Cosmographicum (Cosmographic Mystery) in 1596. This work is significant because it presented the first comprehensive and cogent account of the geometrical advantages of Copernican theory.

Kepler held the chair of astronomy and mathematics at the University of Graz from 1594 until 1600, when he became assistant to the Danish astronomer Tycho Brahe in the observatory near Prague.

Kepler assumed his position as imperial mathematician and court astronomer to Rudolf II, Holy Roman emperor on the death of Brahe in 1601. One of his major works during this period was Astronomia Nova (New Astronomy, 1609), the great culmination of his painstaking efforts to calculate the orbit of Mars. This treatise contains statements of two of Kepler's so-called laws of planetary motion.

The first is that the planets move in elliptic orbits with the sun at one focus.

The second states that a hypothetical line from the sun to a planet sweeps out equal areas of an ellipse during equal intervals of time; in other words, the closer a planet comes to the sun, the more rapidly it moves.

In 1612 Kepler became mathematician to the states of Oberцsterreich (Upper Austria). While living in Linz, he published his Harmonice Mundi (Harmony of the World, 1619), the final section of which contained another discovery about planetary motion: The ratio of the cube of a planet's distance from the sun and the square of the planet's orbital period is a constant and is the same for all planets.

Ta2 / Tb2 = Ra3 / Rb3

At about the same time he began publishing a book that took three years to appear, the Epitome Astronomiae Copernicanae (Epitome of Copernican Astronomy, 1618-1621), which brought all of Kepler's discoveries together in a single book. Equally important, it became the first textbook of astronomy to be based on the Copernican theory, and for the next three decades it was a major influence in converting many astronomers to Keplerian



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