Download 2. Heliocentric Model Of Solar Systems

Our View of the Universe
1. How did early humans view their universe
and create models to explain what he
saw? (click here)
2. How can we explain the real motions of
celestial objects?
(click here)
3. How can we prove Earth rotates on its
axis?
(click here)
4. How was the Heliocentric model
improved?
(click here)
1. First Model of the Universe
Our original view of the universe is based on just looking up
and making observations.
Originally all thought everything revolved around Earth. A
Greek scientist, Ptolemy (150 A.D.), designed a model
which puts Earth at the center and all other celestial objects
orbiting around it.
This model is known as the Geocentric Model of the
universe.
• Ptolemy’s model had to explain the motion that were
being observed. Ptolemy put Earth at the center of the
Universe and then put the known planets at that time
(Mercury, Venus, and Mars) and the Moon and Sun
orbiting around Earth in circular orbits.
• Because of the motions of the Planets, the model had
smaller orbits called epicycles. The model was very
complicated.
• The model was able to help predict where the planets
would be but it was not very accurate.
Geocentric
Model
Mercury
Orbit
Earth
Venus
Sun
Epicycle
Moon
Mars
• The model was able to explain why Mercury and Venus were
only seen during Sunrise and Sunset.
• It also explain the Retrograde Motion of Mars
• Retrograde Motion is the apparent motion that a planet
seems to back up in its orbit.
• As Mars orbited Earth it
also moved in its epicycle
which produce the
retrograde motion.
Earth
Problems with Geocentric Model
• It is not that accurate and had troubled predicting
where celestial objects would be.
• When outer planets were discovered and put into
the model, many epicycles needed to be added to
the planets orbits to show their motions.
• The model became extremely complicated.
• (click here)
2. Heliocentric Model Of Solar
Systems
• Model created by Nicolaus Copernicus (1500 A.D.)
• It put the Sun as the center of a solar system with the
planets including Earth orbiting around the Sun in
circular orbits. It also placed the moons orbiting the
planets.
• To prove it, the model had to explain why Mercury and
Venus are only seen during Sunrise and Sunset, the
retrograde motion seen of the planets, and Earth
rotates on it’s axis.
Heliocentric
Model
Orbit
Venus
Mercury
Mars
Sun
Moon
Earth
Mercury and Venus
• Why we only see
Mercury and Venus
around the time of
Sunrise and Sunset is
because Mercury and
Venus are closer to the
Sun than we are.
• We have to look towards
the Sun to see these
planets.
Retrograde Motion Of Outer Planets
• Retrograde Motion is the
apparent motion that a
planet seems to back up
in its orbit.
• Ptolmey used epicylce to explain this motion.
• Copernicus’ model explains this motion, because Earth
is passing or being passed by other planets in their
orbits and this creates this apparent motion of the
planets going backwards for a brief time.
Retrograde motion of Mars
(click here)
3. Evidence of Earth Rotates on it’s
Axis
• Coriolis Effect
A free flying object will deflect
due to the rotation of the Earth.
• Foucault Pendulum
A free swinging pendulum will
seem to rotate. Actually the
Earth rotates under the
pendulum.
4. Tweaking the Heliocentric model
• After Tyco Brahe passing, Kepler inherited
Tyco’s work.
• From this Kepler was able to create 3
Laws to describe planetary motion.
• These laws are still used today.
First law
Second law
Third Law
Newton’s Law of Gravity
Kepler’s First Law
All planets revolve
around the sun in
elliptical orbits.
The Sun exists at
one of the focal
points of the ellipse.
At the other focal
point is empty space.
Therefore the distance between
the planet and the Sun changes
as the planet revolves around the
Sun.
Eccentricity of an ellipse
Focal Points
Distance between foci
Length of
of major
major axis
Length
axis
Eccentricity =
0
eccentricity
1
(click here)
At the end
Kepler’s Second Law
• Equal Area: As a planet revolves around the
sun it will sweep out an area between two points
equal to the area of another two points providing
it occurs during the same time period.
The planet will change velocity (speed) as it
moves around the Sun.
The closer to the Sun the faster the planet will
travel in it’s orbit.
(click here)
At the end
Kepler’s Third Law
• States that the cube of the mean distance
from a planet to the Sun is proportional to
the square of the planets time to orbit the
Sun.
Example: Neptune
The distance must be in
Astronomical Units
(AUs)1AU =149.6 million km
Time of revolution is 164.8 earth years
164.82 = 27159.04
³√27159.04=30.058 AU
30.058 AU x 149.6 million km = 4496.79 million km.
Time must be in Earth
years.
d3≈t2
Actual distance of Neptune to Sun
Mean distance 4,496 million km or 30.05 AU
(click here)
at the end
Newton’s Law of Gravity
• It is based on the mass of two objects, the
universal gravity constant (G), and the
square of the distance between the two
objects.
-11
Gravity=
Mass1 x Mass2
XG
G = 6.6726x10
distance2
Increase either mass
and you will increase
the gravity
If you change the distance it will
change the gravity by its square.
Meaning if you double your distance
gravity will be 4 times less.