(1571 - 1630) Johannes Kepler was an astronomer, telescope maker, optician and mathematician who lived in
Germany. He worked as a Mathematics teacher at a school in Austria and a court mathematician to Emperor Rudolf II. He was also an assistant to the famous astronomer Tycho Brahe. He is best known for several things including his books "Eponymous laws of Planetary motion", Astronomia nova, Harmonices Mundi and Epitome of Copernican Astronomy. He is also the inventor of the Keplerian Telescope which was a distinct improvement over the Galilean telescope. Keplers telescope used a convex lens at the eyepiece rather than a concave one. This gave the telescope a greater field of vision and better eye relief but it did necessitate a longer focal length.
There were two events in the childhood of Keplers life that had a dramatic impact on his choice to work in astronomy and optics. First, at the age of 6 he observed the Great comet of 1577. Later, at age nine, he witnessed a lunar eclipse.
His first major written work was the Mysterium Cosmographicum (The Cosmographic Mystery) and it was a defense of the Copernican system where the planets revolved around the sun rather than everything revolving around the earth.
His Big Claim to Fame - Kepler is probably most famous for his Laws of Planetary Motion. In these he more accurately predicted the position and movement of the planets because he broke away from the concept that planets moved in circles. He proposed rather that they moved in ellipses. Which we know to be correct.
Law 1: Law of Ellipses - The orbit of each planet is an ellipse.
Law 2: Law of Equal areas - A line drawn from a planet to the sun sweeps out equal areas in equal times.
Law 3: Harmonic Law - The square of the orbital period of a planet is directly proportional to the cube of its average distance from the sun.
This picture shows a keplerian telescope that was built some time around 1673. This particular telescope wasn't built by kepler but it was of the keplerian design. You can see that this type of telescope had an extremely long focal length. This one is about 45 meters in length.
Books by and about Johannes Kepler
Kepler - Definitive biography by foremost scholar offers fascinating erudite picture of great mathematician's scientific accomplishments: formulation of laws of planetary motion, work with optics and calculus, much more. Also detailed chronicle of Kepler's public and personal life (childhood and youth, education, mother's trial as a witch, fear of religious persecution, etc.). Introduction and Notes by Owen Gingerich. Bibliography.