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Mav Mark
11/3/11
When electricity leaves a power plant is it AC or
DC, and is it at high voltage or low voltage?
Observing the Solar
System
Notes
Earth at the Center
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Most early Greek astronomers believed that
Earth was the center of the universe.
They also noticed that a few “stars” in the
sky seemed to follow paths separate from
the others. The Greeks called them planets
from their word for “wanderers.”
The Romans would later label these planets
Mercury, Venus, Mars, Jupiter, and Saturn
after their own gods.
Earth at the Center
• A model of the universe in which Earth
is at the center is called a geocentric
system. In a geocentric system, all
planets and stars revolve around Earth.
Earth at the Center
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The Greek astronomer Ptolemy developed a
complex geocentric model of the universe around
the year 140 CE. Ptolemy’s model seemed to
explain motions in the sky.
Because the planets occasionally appear to go
backwards in the sky, Ptolemy had to come up with
some kind of solution for this motion, so he claimed
that the planets, in their orbits, would make small
circles called epicycles.
Ptolemy’s theories fit so well all of the observations
of the planets and stars, that his model of the
universe would last for nearly 1,500 years, until
nearly the end of the Italian Renaissance.
Sun at the Center
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A system in which the sun is at the center is
called a heliocentric system. Earth and
other planets revolve around the sun in a
heliocentric system.
In 1543, a Polish astronomer named
Nicolaus Copernicus developed a good
heliocentric model of the universe, but still
contained a few flaws.
Despite the fact that he was mostly correct,
his theories would still be rejected for over 50
years.
Sun
at
the
Center
• In the 1600s, the Italian scientist Galileo Galilei
made discovers that supported the heliocentric
model.
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For example, using his telescope, Galileo
discovered the four largest moons of Jupiter
(known now as the Galilean Moons), proving that
not everything orbited Earth.
His observations of a full set of phases for Venus
also supported a heliocentric view of the
universe.
Galileo too was ridiculed for his theories. He was
even put under house arrest by Pope Urban the
VIII for “vehement suspicion of heresy,” where he
would eventually die.
Sun at the Center
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The most accurate measurements of the stars
and planets was made by a Danish astronomer
named Tycho Brahe.
Unfortunately, Brahe was a believer of Ptolemy’s
geocentric vision of the universe. At the same
time, though, he had to concede that some
observations fit a heliocentric view. In a way to
keep both versions, he created a new model of
the universe.
His model came to be known as a geoheliocentric model, or the Tychonic model.
Sun at the Center
• Brahe’s greatest contribution, beside
his very precise observations, was
actually his apprentice, Johannes
Kepler.
• Brahe knew that Kepler was smarter, so
he hid some research from Kepler, and
presented him with minor tasks, such
as figuring out Mars’ orbit, and only
gave Kepler part of his research.
• This would actually allow Kepler to
make the greatest discovery of his life.
Sun at the Center
• After years of study, and Brahe’s
eventual death, Kepler had finally
reached a very controversial
conclusion.
• The orbit of Mars was not a perfect
circle.
• Kepler discovered that not only Mars,
but all of the planets travel in a path in
the shape of a flattened circle, or an
ellipse.
Sun at the Center
•
Kepler used his own calculations, as well
as Brahe’s observations to create his
Three Laws of Planetary Motion:
1. The orbit of every planet is an ellipse with
the Sun at one of the two foci.
2. A line joining a planet and the Sun sweeps
out equal areas during equal intervals of
time.
3. The square of the orbital period of a planet
is directly proportional to the cube of the
semi-major axis of its orbit.
Kepler’s Three Laws
of Planetary Motion
http://solarsystem.nasa.gov/multimedia/videos/Kep
lers_Laws_fullscreen.mov
Modern Discoveries
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Early astronomers only knew of six planets:
Mercury, Venus, Earth, Mars, Jupiter, and Saturn.
Uranus was eventually discovered by William
Herschel in 1781, but he originally though it to be a
comet.
"I don't know what to call it. It is as likely to be a
regular planet moving in an orbit nearly circular to
the sun as a Comet moving in a very eccentric
ellipsis. I have not yet seen any coma or tail to it".
Due to it’s nearly circular orbit, it was later named a
planet, Uranus, after the Greek sky god Ouranos.
Modern Discoveries
• Neptune was discovered in 1846, but
was actually discovered by
mathematical prediction rather than by
direct observation.
• Oddities in the orbit of Uranus led to the
prediction of a large gravitationally
massive object outside of Uranus’ orbit.
Modern Discoveries
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While Herschel was looking in the sky with his telescope
for Uranus, he noticed fuzzy, white patches that he could
not identify. Despite the fact that he didn’t know what they
were, he noted their positions anyway.
In 1923, with the invention of photography, an astronomer
named Edwin Hubble studied these “fuzzy patches.”
Edwin concluded that they were entire galaxies of stars,
each containing their own hundreds of billions of stars.
Before Hubble, we really thought that we were the only
galaxy out there.
The Scientists
http://solarsystem.nasa.gov/multimedia/videos/ssm
_08_The-Scientists-640x360.mov