# 2.1 Do NowTake 15 minutes to complete the do now. Make sure to

```2.1 Do Now
Take 15 minutes to complete the do now. Make sure to write your
name, date, and 2.1 on top of your paper.
Read the Article “New Planet Discovered Similar to Earth” and fill in what
you know about the Kepler planet in the appropriate circle:
Kepler Planet
Earth
Objective
EEn.1.1.1 TSW explain the Earth’s motion through
space (nutation, barycenter (sun's moving), and
precession) by checkpoints.
EQ: How does the Earth move? What is the difference
between precession and nutation?
Kepler’s Laws
Kepler created 3 laws that discussed how our Earth and
the planets move.
Kepler’s 1st Law
of Planetary motion.
st
1
Kepler’s
Law: Law of
Ellipses
Planets move in elliptical orbits with the Sun at one
focus.
Why does the Earth move in
an ellipse?
● An ellipse is an oval-shaped figure whose shape is
determined by 2 foci.
● The Sun is at one focus planet’s orbit; the second focus
is empty because of the gravitational pull.
How does the Earth move?
1.Rotation
2.Revolution
3.Precession
4.Nutation
Rotation
● Rotates = spins.
● 1 rotation=24 hours/ 1 day
Looking at the picture below, why is the left hemisphere
experiencing a warm day and the right hemisphere
experiencing a cooler night?
DAY
warmer
NIGHT
cooler
Revolution
•Revolves (orbits around) the
sun
•1 revolution= 365 days/ 1
year
Quick Quiz #1
What is the difference between rotation and revolution?
A. Rotation is when the Earth orbits around the sun and
Revolution is the Earth spinning.
B. Rotation gives Earth 1 year (365 days) and Revolution
gives Earth 1 day (24 hrs)
C. Rotation is when the Earth spins and Revolution is
when the Earth orbits around the Sun.
D. Rotation moves in an ellipse and Revolution moves in
a circle around the sun.
Precession
● The change in direction of the axis of the Earth, but without any
change in tilt
-Like the wobbling motion of a spinning top
● 1 precessional cycle: approximately 26,000 years
Just like a spinning top!
http://vimeo.com/3110658
Quick Quiz #2
Which is the best explanation for precession?
A. Precession is how the Earth revolves around the sun
B. Precession is how the Earth spins
C. Precession takes 1 day to make a rotation
D. Precession is the change in direction of the Earth’s axis
as it rotates
Nutation
What do you notice
of the Earth?
Nutation
● The wobbling/swaying motion during the precession of
our axis.
● This causes a 1 degree change in the tilt of the Earth’s
axis.
Quick Quiz #3
What is the best explanation of nutation?
A. The spinning of the Earth
B. The wobbling of the Earth’s axis
C. The change in direction of the Earth’s axis
D. The orbiting of the Earth around the sun
Kepler’s 2nd law
A planet that speeds up when it is closer
to the Sun because of the Sun’s
gravitational pull.
Animation
A planet travels the same distance in the
same time and but at different speeds
(velocities).
Identify the following on the picture: which
side is faster?
Quick Check
1. Therefore, Earth moves
________________________ (faster/slower) in
summer than in winter, so summer in the Northern
Hemisphere must be
___________________________ (longer/shorter)
than winter.
2. Isaac Newton later determined that the force of
GRAVITY holds the planets in orbit around the Sun.
When a planet is closer to the Sun, the force of the
Sun’s gravitational attraction on the planet is
_________________________ (stronger/weaker)
than when the planet is farther from the Sun.
Kepler’s law and Barycenter
Barycenter- is the center of mass between two points.
All bodies (planets, the sun) in our solar system revolve
around a barycenter.
Center of Mass
Unbalanced
Balanced
So what does this mean?
● Yes, the sun is the center of the solar system.
● But the sun and planets are BOTH revolving around the
barycenter (the center of mass between them).
http://en.wikipedia.org/wiki/File:Orbit4.gif
Where is the barycenter
located?
For two objects that are of different masses, the
barycenter is CLOSER to the one with MORE mass.
Barycenter Lab
Barycenter Lab
Barycenter Lab
Barycenter Lab
Barycenter Lab
Barycenter Lab
Complete the results and conclusion section of your lab writeup.
This will be worth a 30 point project grade. Remember to write
in complete sentences!
Kepler’s 3rd Law of Planetary
Motion
The time it takes to REVOLVE around the Sun= the distance from the Sun.
The farther you are from the sun, the longer it takes to get around the sun.
Just like a track!
For example: Earth
The Earth takes ___________ (longer/shorter) than
Mercury to revolve around the sun.
The Earth takes _____________ (longer/shorter) than
Mars to revolve around the sun.
Kepler's third law of planetary motion
describes a relationship between the
A. Shape of orbit and location of Sun.
B. Speed of the Earth and its position in
orbit.
C. Distance from the sun and length of
year.
Kepler's Laws is true?
A. A planet moves faster when its orbit is close to
the sun.
B. The planet travels faster when it is away from
the sun.
C. Planets travel in circular orbits
Exit Ticket
Complete the Earth section of the Do Now.
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