Transcript 13.3
Modelling Celestial Motion
Using Models
Designers and engineers use models to
help them solve problems without having
to construct the real thing.
Using Models
They may be cars.
Using Models
They may be
computer generated
ship models.
Using Models
Or they may plan out
entire cities.
Astronomical Models
Astronomer also use
models. They use
them to explain things
like celestial motion.
Two Main Models
There were two main models devised to
explain the motion of the Sun, Moon,
planets and stars.
One was the geocentric, or Earth-centered
model.
The other was the heliocentric, or Suncentered model.
Geocentric Model
As early astronomers
looked up into the
night sky they saw
objects in the sky
move from east to
west.
Geocentric Model
Early Greek
astronomers such as
Aristotle and Ptolemy
used concentric
circles (circles within
circles) to explain the
motion.
Geocentric Model
As a result they
developed the
Geocentric or EarthCentered Model to
explain this motion.
Geocentric Model
Let’s slow things
down…
Turn to p.435
Geocentric Model
How did the model
explain retrograde
motion?
Simple, some planets
had orbits within their
orbits.
They were called
epicycles.
Geocentric Model
As Mars, Jupiter and
Saturn orbited Earth,
they made circular
motions around their
path.
This was the apparent
cause for the
retrograde motion.
Geocentric Model
Physical
representations such
as this 3m model
could predict phases
of the Moon and
eclipses.
Geocentric Model
The model worked so well it remained the
dominant theory for nearly 2000 years.
Heliocentric Model
The heliocentric
model of the solar
system was a
revolutionary idea at
the time.
It placed the sun at
the center of our solar
system.
Heliocentric Model
The heliocentric model of the solar system
began to take root during the
Renaissance.
The Renaissance was a period from 13001500 when scholars and scientists began
to look at things in a different way.
Heliocentric Model
The heliocentric
model was proposed
by Nicholas
Copernicus, a Polish
astronomer.
Heliocentric Model
Copernicus theorized
that the Sun, not the
Earth, was at the
center of our Solar
System.
He also believed that
the planets orbited
the sun on what he
called the Solar Plane.
Heliocentric Model
An Italian astronomer,
Galileo Galilei,
furthered the work of
Copernicus.
Heliocentric Model
Using more advanced
equipment, such as
more accurate
telescopes, he was
able to observe more.
Heliocentric Model
Galileo determined
that Jupiter had
moons and that
Venus had phases,
just like Earth’s Moon.
All this supported the
Heliocentric Model.
Heliocentric Model
The Heliocentric
Model still did not
predict celestial
events as accurately
as the Geocentric
Model.
German
mathematician
Johannes Kepler
discovered why.
Heliocentric Model
Kepler discovered that
the planet’s orbits
were not circular but
ellipses.
This strengthened the
Heliocentric Model.
Heliocentric Model
Isaac Newton’s
discovery of gravity
only strengthened the
Heliocentric Model
more.
Now there was a
reason why the
planets moved the
way they did, the
Sun’s gravity.
Heliocentric Model
In 1846 the Heliocentric
Model was used in the
discovery of a new
planet.
Based on the movement
of Uranus it was
theorized another
planetary body existed.
When telescopes were
trained on the predicted
spot they discovered
Neptune.
The Solar System Today
With advanced
telescopes and
unmanned space
probes we have been
able to learn even
more.
The Solar System Today
Today we know we
share our solar
system with asteroids,
meteors and comets.
All these objects are
in orbit around the
sun.
Homework
Please finish reading section 13.3
Complete questions #1-5
Vocabulary
Celestial Sphere
Solar Plane
Solar System