Johannes Kepler

Johannes Kepler is a prominent figure when speaking about the dawn of astronomy. His life is one that is full of twists and turns, and Cosmos goes into detail about numerous aspects of his life. Ill be giving a brief description of his life, and his contributions to the field of astronomy. 


Kepler was born December 27, 1571 and as a boy he was sent to Protestant seminary school to learn how to become a clergy man. Kepler realized at an early age that the life of a zealot was not for him. He was instead driven by space, which was his biggest curiosity and his muse. Kepler was a gifted mathematician, and used his talent to make observations about the stars that was on par with the greats of the time. He  has a small fling as being a teacher; unfortunately a miserable failure. Kepler has been said to have a gifted mind, however its not always the smartest people that make the best teachers. He was horribly inept at getting his ideas across to his students, most of which dropped from his classes. He quickly left the classroom and went into the laboratory, asking for a grant from the duke of wurtemberg. His proposal was unfortunately rejected, which is when he met another prominent figure of the time, a schoolteacher named Tycho. Tycho was much better off then the poor Kepler, owning numerous instruments all of which costed more the Kepler life earnings. Kepler and Tycho did end up working together at some point, its a shame that it only happened after Tycho died. Tycho had given Kepler some key data that was needed for him to finish one of his theories. Kepler published many works about physics and astronomy. Johannes Kepler died in Regensburg in 1630. 

Kepler is best known for his 3 laws on planetary motion. 

                                          Planets move in ellipses with the Sun at one focus.

This is a good example of what Kepler proved; that the eclipse is an accurate representation of a planet, and the circle is what was previously thought for it to be. 

The law of equal areas 

The law of equal areas states that a line that connects a planet to the sun sweeps out equal areas in equal times. This basically means that an equal amount of area will be covered when an equal amount of time has passed at any 2 distances in the planets orbit. 

The law of periods

line that connects a planet to the sun sweeps out equal areas in equal times. This essentially means that it will take shorter amounts of time for planets with smaller radii to circle the sun. Thus why mercury has an 88 day long year

Chapter one- The shores of the cosmic ocean

In the first chapter of cosmos Carl Sagan has some very interesting things to say about the ancient philosophers and their impacts on our knowledge of space. One person whom he details is a philosopher by the name of Eratosthenes. Eratosthenes was the first person to estimate the circumference of the earth and he did so in a pretty ingenious way. There were two stakes on the ground; one in the city he was residing in, Alexandria, and another in a city which was 900 miles from him, Sienna. At exactly noon, both him and his assistant measured the angles of the shadows cast by the stakes. Using this, he was able to estimate the circumference of the earth.

This diagram pretty well describes what the experiment Eratosthenes was trying to do.

Not only did this tell Eratosthenes the circumference of the earth, but it also told him with certainty that the world 100% had to be round. With this knowledge, he made it safe for others to venture far into the unknown and sail west as far as they could, and when you think about it, adventurers sailing westward is  like us exploring space. People venturing out into the unknown just to see whats out there. Its interesting seeing these parallels in history like this.

Introduction/ Preface

Cosmos, by Carl Sagan is one of the best selling science books published in the English language.  After being published in 1980, a television series depicting some of the themes of the book was put into production. The series was put into production and run around the same time that the book was published. It's been said that the book and the movie were meant to be experienced in tandem, knowing that i will be both reading the book and watching the series at to get the entire experience of the Cosmos.