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What's This?Johannes Kepler (December 27, 1571 – November 15, 1630) was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican Astronomy.

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Kepler’s laws of planetary motion were his greatest contribution to science. These laws had an enormous impact on scientific thinking, providing the groundwork for Sir Isaac Newton’s later work on universal gravitation. However, Kepler made many other contributions to science as well. He discovered a new star (a supernova); he analysed how the human eye works; he made improvements to the telescope, and made other contributions in the field of optics.

Other speakers examined Kepler’s theory of music, his philosophy of nature, his notion of experiment, as well as his astrology work.

refused to sign the Formula of Concord. Because of his refusal he was excluded from the sacrament in the Lutheran church. This and his refusal to convert to Catholicism left him alienated by both the Lutherans and the Catholics. Thus he had no refuge during the Thirty-Years War.

Kepler believed that nature followed numeric relationships since God created it according to "weight, measure and number." Kepler used the same idea in describing geometry (the study of points, lines, angles, and surfaces). Kepler's second work, the Epitome astronomiae Copernicanae (published 1618–21), proposed a physical explanation of the motions of planets, namely, "magnetic arms" extending from the sun.

He negated that people’s lives depend on the stars. He also studied the long term accuracy of astrology as such it was recorded that trusting on astrology alone would entail risks.

In De fundamentis astrologiae certioribus (1602) he declared his purpose of preserving and purifying the grain of truth which he believed the science to contain. In 1604 Astronomia pars Optica appeared, in which he treated both atmospheric refraction and lenses. In 1606 he published De Stella Nova which was about the new star that had appeared in 1604.

According to Kepler, each branch of knowledge must finally be reduced to geometry if it is to be accepted as knowledge in the strong sense. Thus, the new principles he was elaborating over the years in astrology were geometrical ones. A similar case occurs with the basic notions of harmony, which, after Kepler, could be reduced to geometry.

The speed at which any planet moves through space is constantly changing. A planet moves fastest when it is closest to the sun and slowest when it is furthest from the sun. Yet, if an imaginary line were drawn from the center of the planet to the center of the sun, that line would sweep out the same area in equal periods of time.

If he could find multiple observations of Mars separated by this interval of time, he could observe how the angle between Earth and Mars changed and thus learn something about the parameters of Earth's orbit.

Using trigonometry Kepler discovered the relative distances between Earth, Mars, and the center of Earth’s orbit, taking the Earth-Mars distance as a constant.

Kepler's first Law: The orbit of a planet about the Sun is an ellipse with the Sun's center of mass at one focus.

Kepler's second Law: A line joining a planet and the Sun sweeps out equal areas in equal intervals of time.

Kepler's third Law: The squares of the periods of the planets are proportional to the cubes of their semi-major axes.

Kepler tried all sorts of mystical notions to describe planetary orbits, using the Platonic solids and musical analogies. Spread out through his voluminous calculations in Astronomia Nova, however, were three gems: Kepler's laws of planetary motion.

it was poor, myopic Kepler who fathomed the anatomy of the eye, founded the science of optics, and figured out, through years of trial and error, what courses the planets follow.

But his evident intelligence earned him a scholarship to the University of Tübingen to study for the Lutheran ministry. There he was introduced to the ideas of Copernicus and delighted in them. In 1596, while a mathematics teacher in Graz, he wrote the first outspoken defense of the Copernican system, the Mysterium Cosmographicum.

On this day in 4977 B.C., the universe is created, according to German mathematician and astronomer Johannes Kepler, considered a founder of modern science.

Kepler's achievements played a critical role in bring about the unprecedented explosion of discovery and advancement that characterized the Scientific Revolution.