The planets revolve around the sun in elliptical orbits" This was one of the most remarkable discovery in the field of astronomy, and do you know that who was the man behind this ? He was none other than **Johannes Kepler,** who is having his 447th birth anniversary today!

Johannes Kepler, The father of astronomy, having the three laws of planetary motion named after him, was born on December 27,1571, in Weil der Stadt, Württemberg, in the Holy Roman Empire of German Nationality. As a child, Kepler was often in poor health. However, he never failed to astonish the guests at his grandfather's inn with his incredible arithmetic abilities.His mother, Katharina, tried to convey her love of the natural world to her son by taking him out at night to show him interesting things in the heavens, including a comet and a lunar eclipse. However, childhood smallpox left him with weak vision, limiting his ability in the observational aspects of astronomy. Still, as dedicated he was,he was set on a course which eventually transformed our understanding of the solar system and the universe.

Kepler's early education was in a local school and then at a nearby seminary, from which he went on to enrol at the University of Tübingen. He proved himself to be a superb mathematician and earned a reputation as a skilful astrologer, casting horoscopes for fellow students. Kepler learned both the Ptolemaic system and the Copernican system of planetary motion. He became a Copernican at that time. In a student disputation, he defended heliocentrism, maintaining that the Sun was the principal source of motive power in the universe.

In 1600, a wealthy Danish astronomer, Tycho Brahe invited Kepler to work with him. Of all the planets, the predicted position of Mars had the largest errors and therefore posed the greatest problem

Hence, Kepler was assigned the task of solving the mystery of Mars, one of the most puzzling problems in astronomy at that time.The Martian problem, which Kepler said he would solve in eight days, took nearly eight years, but finally by using tycho's observations, Kepler was able to solve this problem and eventually gave his three laws of planetary motion, conventionally designated as follows:

- The planets move in elliptical orbits with the Sun at one focus.
- A line between the sun and the planet sweeps equal areas in equal times, ie. the time necessary to traverse any arc of a planetary orbit is proportional to the area of the sector between the central body and that arc.
- There is an exact relationship between the squares of the planets’ periodic times and the cubes of the radii of their orbits.

Kepler's third law led Newton to his law of gravitation. Hence it would not be wrong to regard Kepler as the founder of celestial mechanics!

Apart from his laws of planetary motion, Kepler also did important work in optics,he developed a novel explanation for the behaviour of light in the newly invented telescope.He created eyeglasses for both near and farsightedness, and explained how a telescope worked. He described images and magnification, and understood the properties of reflection.

Kepler discovered two new regular polyhedra in 1619. He gave the first mathematical treatment of close packing of equal spheres which led to an explanation of the shape of the cells of a honeycomb in 1611.Kepler also gave the first proof of how logarithms worked and devised a method of finding the volumes of solids that can be seen as contributing to the development of calculus.Kepler suggested that the sun rotates, and created the word "satellite." He tried to use his knowledge of the distance Earth travels to measure the distance to the stars. Kepler also established that the tides were caused by the moon, hence correcting Galileo's views about the reason of tides. Kepler is also credited for calculating the birth year of Christ.

Johannes Kepler died in Regensburg in 1630, while on a journey from his home in Sagan to collect a debt.Throughout his life, Kepler was a profoundly religious man. All his writings contain numerous references to God, and he saw his work as a fulfilment of his Christian duty to understand the works of God. Moreover, Kepler was convinced that God had made the Universe according to a mathematical plan.Johannes Kepler definitely played a key role in the profound changes in human thinking that took place during the scientific revolution. Kepler's laws not only describe the planetary motion, but also help in determining the orbits of satellites and Space stations.Hence, it would not be wrong to say that this man changed the course of astronomy!

Happy Birthday Legend!