What are Kepler's three laws? Why are they significant?

Kepler's first law states that the planets travel around the sun in elliptical orbits with the sun located at one focus. This was significant because, until Kepler, it had been firmly believed that the planets traveled in circular orbits. No one was pleased with the aesthetically distasteful idea of ellipses. The second law, which Kepler discovered first, states that as the planets travel around their orbits, they sweep out the same amount of area per unit of time, no matter where they are on the orbit. Like Kepler's first law, this second law destroyed a long-held belief. Astronomers had always assumed that the planets traveled with a uniform speed – Kepler proved that the speed varied as the planets traveled around the orbits. It was only the area covered that remained uniform. Finally, the third law states that the cube of the distance a planet's orbit is from the sun is directly proportional to the square of the period, or time it takes the planet to travel around the sun. This was the first time anyone had thought to question the relationship between a planet's distance from and speed around the sun. The equation was nothing more than an interesting mathematical relationship to Kepler; it wasn't until Newton created the theory of universal gravitation that the meaning of this relationship became clear.

What was Kepler's theory of the perfect solids?

In 1595, Kepler had an epiphany. He was searching
for a rationale for the number and spacing of the planets, and
he believed he had found it in the perfect solids. A perfect solid
is a three dimensional figure, such as a cube, whose sides are
all identical. There are only five perfect solids, each of which
can be inscribed in and circumscribed around a sphere. Kepler believed
that the orbits of the six known planets could be fit around the
five regular solids. He felt he had seen into the mind of God and
finally understood the structure of the universe. He described
this theory in his first book, the *Mysterium Cosmographicum.* Kepler's
theory was incorrect, but developing this idea became his motivation
for a lifetime of astronomical study.

What role did Tycho de Brahe play in Kepler's life?

Had Kepler not crossed paths with the famous
astronomer Tycho, he may never have formulated any of his three
laws. Kepler needed Tycho's incredibly accurate and comprehensive
astronomical observations in order to fully develop his own system.
In 1600, Kepler traveled to Prague to work in Tycho's lab. Although
he was there for only a year before Tycho died, that year marked
a turning point in Kepler's life. Tycho was a tyrannical boss,
but he provided Kepler with the two tools Kepler would need to
revolutionize astronomy: detailed observations and the orbit of
Mars. Tycho assigned Kepler to figure out the shape of the orbit
of Mars. The thorny problem would take him over half a decade to
solve, but the struggle was worth it. Only in the irregular orbit
of Mars could Kepler have discovered the fundamental properties
of the planetary orbits. Once Tycho died, Kepler took his astronomical
observations from the laboratory and went to work on the Mars problem.
Eight years later, he published his results in the *Astronomia
Nova*. Tycho had hoped that Kepler would apply his theories
to the Tychonic system of the universe, but Kepler stayed true
to the Copernican system. Kepler used the Copernican system to
develop the *Astronomia Nova*.

What was the difference between the original Copernican system and Kepler's interpretation of it?

What were some of the events that caused Kepler to feel he'd had a miserable life?

Discuss the contents and importance of Kepler's three
major works, the *Mysterium Cosmographicum,* the *Astronomia Nova,* and
the *Harmonice Mundi*.

What was Kepler's impression of his own work? Which of his achievements did he most value and which did he overlook?

Kepler is one of the founding fathers of the Scientific Revolution, along with Copernicus, Galileo, and Newton. What is the importance of each of them in Kepler's life and work?

Why can it be said that Kepler rejoined astronomy and physics? Why is this significant?

Discuss the importance of religion in Kepler's life and work.

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