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The
sun has a family of
nine planets moving around it due to its
gravity. Along with these planets the solar
system has comets, asteroids,
planetoids, and moons
orbiting around planets.
HISTORY
Science
and our view of the world change only when we
are presented with some observation we can't
explain. Early Greek philosophers believed that
Earth was at the center of the Universe and all
other celestial bodies moving around it.
Eudoxus, a
mathematician who lived
in the
fourth century B.C., was one of the first people
to propose this theory. Eudoxus’ version of
the theory was elegantly simple: God is perfect,
the only perfect forms are circles, therefore
the Sun and planets must move in circles around
the Earth. Claudius Ptolemy, a Greek scholar who
lived in Alexandria, Egypt, around 140 AD noted
that there were some problems with the theory,
however. Careful observations showed that the
planets did not quite move in perfect circles.
Faced with an observation that couldn’t be
explained with current theories, Ptolemy
modified Eudoxus’ theory and replaced his
simple circles with a complicated system of
"epicycles", circles that interlock
like gears in a complex machine. Ptolemy’s
theory could describe and predict the motions of
the planets with an accuracy never before
achieved. For almost 1,400 years, until the 16th
century, Ptolemy’s theory was considered to be
the only theory was considered to be the only
correct theory of the Universe. The theory was
endorsed by the Catholic Church, which declared
any other explanation for the planets’ motions
to be heresy and punishable by death.
Ptolemy’s
theory only had one problem:it was wrong. One
hundred years after Eudoxus, the astronomer
Aristarchus watched the shadow of the Earth
sweep across the surface of the Moon during a
lunar eclipse. His observations showed that the
Sun had to be much larger than the Earth, and he
felt that it was not likely that a large Sun
would rotate around the smaller Earth. He
proposed instead that the Earth revolves around
the Sun. He was condemned for heresy because of
his theory and all of his writings were rounded
up and destroyed. The only reason we know
anything about Aristarchus at all is because he
is mentioned inthe writings of great
mathematician Archimedes. No other scientist was
willing to risk the wrath of the church by
mentioning the astronomer's work. In 1953,
nearly 2000 years later, however, Aristarchus'
theory was taken up by Polish doctor, lawyer and
part-time astronomer Nicolaus
Copernicus.Copernicus' careful observations
could not be explained by Ptolemy's theory. Only
if the sun were at the center of the SOLAR
SYSTEM could this data make sense. Once again,
because of new observations, new science and a
new worldview was born.
But
Copernicus' theory still could not explain the
strange motion of Mars.
In 1600 Tycho Brahe had undertaken the careful
study of Mars' orbit. Tycho was perhaps the
greatest observational astronomer the world has
ever known. We can make more accurate
observations today only because we have more
accurate instruments. Tycho was world famouswho
toured the palaces of Kings and other nobility
all over Europe. Tycho had given his student, a
German mathematician named Johannes Kepler, the
task of creating a mathematical description of
Mars' orbit.  Tycho, however, was very
protective of his data, as are many scientist
today. He would throw out an observation over
dinner in casual conversation, which Kepler
would frantically scrawl down in a notebook that
he kept under the table. When Tycho finally died
several years later, Kepler broke into tycho's
safe and stole all of his data. Tycho's family
demanded the documents to be returned, and
Kepler did so- but only after he had made exact
copies of all the precious data. Kepler, like
most of his fellow scientists, felt certain that
the planets traveled in perfect circles. After
years of struggling with Tycho's observation of
Mars, however, he finally reached the
inescapable conclusion that all the work done
before him was wrong: the planets move in
ellipses, not circles. In addition, he
discovered two other laws of planetary motion
that he published in 1609. Thanks to Mars, we
now understood not only its motion but the
motion of the entire SOLAR SYSTEM as well.
SOURCE-JPL(NASA)
& ASU.
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