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On December 27, 1571, in Weil der Stadt under the Holy Roman Empire, Johannes Kepler was born. The Reformation was a time of religious and military conflict, and during the 16th century, the region was a network of principalities. His father, Heinrich, a mercenary, died when he was five leaving his mother, Katharina, an herbalist, to raise him. All of his life, Kepler would walk the line between potential religious persecution and scientific advancement in a variety of fields. In the end, he would be known as one of the most influential scientific minds in history.

01## Childhood Challenges

Kepler was a sickly child. His hands were weak, and his eyesight was permanently impaired by smallpox. However, he was a great student who astonished people with his abilities to solve numerical problems. His mother introduced him to her love of the natural world, and that included allowing him to stargaze and watch lunar eclipses. That encouragement would greatly influence his career.

02## Studies

At 13, Kepler studied at Maulbronn seminary, and when he was of age, he went to the University of Tubingen. There, he took courses, such as theology and philosophy with the intention of becoming a minister. But his excellence in Mathematics couldn't be ignored. He was identified as being intellectually and mathematically capable of tackling the work of Nicolaus Copernicus, who formulated a model that had the Sun at the center of the universe. Kepler's interest in Astronomy grew, and at the age of 23, he became a lecturer in astronomy and mathematics at a school in Austria.

03## Mysterium Cosmographicum

In 1595, Kepler was introduced to Barbara Muller, a twice-widowed heiress, and daughter of a successful mill owner. The match was initially opposed, due to Kepler's poverty, but with the success of his Mysterium Cosmographicum, his book supporting the Copernicus' heliocentrism, the match was approved. They married in 1597. However, Martin Luther and the Catholic church were against this heliocentric belief, as it was seen as heresy during the time. To reduce the risk of persecution, researchers found that Kepler and his wife coded their correspondences.

04## Tycho Brahe

In search of a new position that would augment his understanding about the paths of the planets, Kepler contacted Tycho Brahe, a wealthy Danish nobleman who had been appointed Imperial Mathematicus at Prague. Brahe had built an observatory to study the motions of the planets and subsequently invited Kepler to be his assistant in 1600. But Brahe was suspicious and only shared certain notes. He assigned Kepler to study the planet Mars, and that fortuitous assignment was the missing information Kepler needed to better understand how the solar system functioned. Tycho Brahe died in 1601, making Kepler his logical replacement. As an imperial mathematician, he gained full access to Brahe's notes which helped him formulate his most famous discoveries.

05## Kepler's First Law

Kepler's First Law of Planetary Motion came in 1609, and it states that a planet's orbit is elliptical in shape with the Sun as one of two foci. The formula is expressed as a ratio of the semilatus rectum, a geometrical chord, over the constant one plus the eccentricity of the ellipse, its shape, multiplied by the cosine of the angle of planet's current position from its closest approach, or, r = p / (1+ ε*cosθ).

06## Kepler Second Law

Kepler's Second Law of Planetary Motion came soon after and describes how fast the planet travels in an elliptical orbit around the sun. It explains how the line between one point of the foci, the Sun, and the planet sweeps equal areas in equal lengths of time. This means that the closer the planet is to the sun, the faster it goes, and when it recedes, it goes slower.

07## Kepler Third Law

Kepler's Third Law of Planetary Motion came in 1618. This one tries to describe how the distance of the planets and the sun relate to their orbital periods. It states that the square of a planet's revolution period is directly proportional to the cube of the planet's average distance from the Sun. This law applies to all planets.

08## His Final Years

From 1615 onward, Kepler's mother stood accused of sorcery. Five years later, he successfully defended her, securing her acquittal and release. She died the following year, due to the effects of the torture she endured. In 1626, he was forced to leave Linz, Austria with this second wife, Susanna, and their children due to the violence of the Thirty Years' War. He published books, the last being his Tabulae Rudophinae in 1628, which augmented Tycho Brahe's astrological findings and provided planetary tables. After falling ill while traveling, Johannes Kepler died on November 15, 1630.

09## Optics Invention

While Johannes Kepler was known for astronomy and mathematics, he was also an inventor. Thanks to his work in exploring the stars, he invented the Keplerian Telescope in 1611 and is considered an improvement over Galileo's design. Kepler used a convex lens, instead of a concave one, that provided a wider field of view and left room to reach higher magnifications.

10## Influence on Isaac Newton and Edmond Halley

Two of the many notable scientists that were influenced by Kepler's work were Sir Isaac Newton and Edmond Halley. Newton's Universal Laws of Gravity and Laws of Motion provided a physical explanation of Kepler's empirical laws. Edmond Halley was Newton's contemporary and used Kepler's Laws to calculate the orbit of comets, one of which is named after him.

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