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Do Now
What is the big bang theory?
2. What is some evidence to support the big
bang theory?
3. What is a red shift and what does that tell us
about distance of objects in space?
4. Explain in your own words what Hubble’s
Law states. Hint: think about your lab from
last class
1.
The Earth’s Role in our
Solar System
https://www.youtube.com/w
atch?v=5c_lL6I3OaA
The Earths role in the Solar
System

http://www.youtube.com/watch?v=5c_lL
6I3OaA
Objective
 SWBAT explain how the earth moves around
the solar system by analyzing Kepler’s Laws,
precession, nutation, and barycenter.
Check this Kid Out…
http://www.youtube.com/watch?v=QWPeLO02H0&feature=youtu.be
Notes on the Universe
 The universe is made of galaxies which are
made of many stars. Some stars have
planetary systems similar to our solar system.
Earth is a satellite planet of one particular
star (our sun)
The (whole) Earth moves in 3
ways.
The Earth:
1.Rotates (Rotation)
2.Orbits
3.Revolves (Revolution)
The earth rotates on its
axis.
• Rotates = spins.
• The earth makes 1 full rotation
every 24 hours.
The axis of the
Earth is tilted
at an angle of
23.5 degrees.
The axis
always points
towards the
North Star.
We have day and night
because of the Earth’s
rotation.
DRAW A PICTURE OF THE EARTH
TILTED ON ITS AXIS…
The Earth also revolves
around the sun in an
elliptical orbit.
The earth makes one full revolution around the
sun every 365.25 days.
365 days = 1 year
Kepler’s First Law
Law of Ellipses
 Each planet takes an elliptical path
around the sun

st
1 Law: Law of Ellipses
The path of the
planets around
the sun are
elliptical in
shape with the
center of the sun
being located at
one focus
The shape of
the ellipse is
determined by
the location of
the two focus
points!
Kepler’s Second Law
Law of Equal Areas
 Planets travel faster when they are close
to the sun and slower when they are
farther away from the sun

nd
2 Law: Law of Equal Areas
This law states that an imaginary line
from the sun to a planet sweeps out
equal areas in equal time intervals
nd
Kepler’s 2 Law of Planetary Motion
Are they the SAME?

The short wide glass is holding the SAME amount of
water as the tall skinny glass!
Planet moves FASTER in orbit when
CLOSE to the SUN, and SLOWER in orbit
when FAR FROM the SUN
GRAVITATIONAL PULL
WHY?
Kepler Animation
https://phet.colorado.edu/en/simulation/gra
vity-and-orbits
Kepler’s Third Law

The amount of time needed for a planet
to revolve around the sun is proportional
to the planet’s distance from the sun
Kepler’s 3rd Law
Kepler’s Three Laws of Planetary
Motion (A Summary)
1. Each planet takes an elliptical path around
the sun
2. Planets travel faster when they are close to
the sun and slower when they are farther
away from the sun
3. The amount of time needed for a planet to
revolve around the sun is proportional to the
the planet’s distance from the sun
A
B
C
Precession
 The direction this axis of a planet is pointing in
will change, but the tilt will not change.
 This will change the stars near the pole but will
not change the seasons (as long as the angle
of the tilt, 23.5 in the case of Earth, stays the
same)
Precession Animation

http://www.youtube.com/watch?v=CUZO
XczMfMo
Nutation
 Nutation happens when the axis of a planet
starts to wobble (do the wobble!)
 The angle of the axis will change during nutation
½ degree one direction or the other
 Nutation happens over the course of 18 years
 Nutation is a direct result of the moon (or
moons) of a planet
Barycenter
 A barycenter is the point between
two objects where they balance
each other (For example, the
middle balancing point on a scale).
Barycenter Example
 For example, the moon does not orbit
the exact center of the Earth, but a point
on a line between the Earth and the
Moon approximately 1,710 km below
the surface of the Earth, where their
respective masses balance.
 This is the point at which the Earth and
Moon orbit as they travel around the
Sun
Do Now
Draw a picture of the Earth on it’s axis.
At what degree is it tilted?
2. Describe Kepler’s first law.
3. What does the law of equal areas
state?
4. Draw a picture depicting his 1st and 2nd
law.
5. Describe Kepler’s third law.
1.
Barycenter Animation
 http://www.youtube.com/watch?v=uG
BANgbRkws

http://www.orbitsimulator.com/gravity/arti
cles/barycenter.html
Application & Critical Thinking
10 minutes
Exit Ticket: 11 points
1. Draw the shape of Earth’s orbit around the sun.
(1 pt)
2. Explain why Earth takes the path you drew in
question #1. (1 pt)
3. What is the angle of the Earth’s tilt on its axis? (1
pt)
4. Explain what Kepler’s law tells us. (1 pt)
5. Explain why the sun is always in motion. Use both
the sun and Earth in your example. (1 pt)
6. Explain how Earth moves about the solar system
(be sure to use rotate, revolve, nutation,
precession, and barycenter, in your response).
(5 pts)
Today’s Exit Ticket: 11 points
1. Draw the shape of Earth’s orbit around the sun.
(1 pt)
2. Explain why Earth takes the path you drew in
question #1. (1 pt)
3. What is the angle of the Earth’s tilt on its axis? (1
pt)
4. Explain what Kepler’s law tells us. (1 pt)
5. Explain why the sun is always in motion. Use both
the sun and Earth in your example. (1 pt)
6. Explain how Earth moves about the solar system
(be sure to use rotate, revolve, nutation,
precession, and barycenter, in your response).
(5 pts)