QQ: Name the planets in our Solar System in order moving away from the Sun. What is the largest planet? What is the smallest planet? Which planet is closest to Earth’s size? What is the shape of the path of the planets’ orbits?

Today’s Objective: I can use Kepler’s Laws to explain the way Earth moves through the Solar System.

Project Approval Sheet Projects Due Monday 9/26…

Astrolabe data: You can collect it on the weekend if it is easier to get a reading.

What’s the big deal about gravity?

Gravity the attraction between every two objects, no matter how big or how small.

Balance point is middle Balance point is not middle

Balancing point around barycenter Center of mass between two objects Balancing point around which planets orbit

Precession The change in direction of the Earth on its axis. Changes which stars we see at night depending upon the season summer winter

What does that mean for Earth?

Nutation The slight wobbling of Earth’s axis as it changes positions ½ degree every 18 years

Discovering Kepler’s Work Follow instructions carefully Work with your group Everyone participates equally

* Tie string that is 8 cm long in a circle * Place white paper board and hold it down with push pins 3 * Place two push pins 3 cm apart * Wrap string around pencil

Kepler’s first law: 1. Planets move in an elliptical orbit (path)

Kepler’s First Law Pin Pin String Orbit Line

Modeling the Shape of an Orbit

2. A planet travel’s faster when it is closer to the sun. Kepler’s 2nd law: 2. A planet travel’s faster when it is closer to the sun. Each area is covered During equal Time periods

Farthest point from Sun b = 40 h = 10 A = ? b = 20 h = 20 A = ? Aphelion: Farthest point from Sun Perihelion: Closest point to Sun Area is same

Earth is farthest from the Sun Aphelion: Earth is farthest from the Sun 152 million km About July 4th

Earth is closest to the Sun Perihelion: Earth is closest to the Sun 147 million km About January 3

Modeling the Speed of a Planet

Kepler’s 3rd law 3. The distance a planet is from the sun affects how long it takes to revolve around the sun.

Comparing Speeds of Planets

Creating the orbits of other planets Move the center pins: 4 cm apart 5 cm apart 6 cm apart 7 cm apart

When the pins were 3 cm apart, one could represent the Sun and the other the barycenter between the Sun & Jupiter.

Imagine one pin is the Sun and the other is the barycenter between Sun & Earth. Would you move the pins further apart or closer together? Why?

Test your hypothesis…. Push the pins close together so they are touching. The barycenter between Earth and Sun is near the edge of the Sun. If one pin is the Sun & the other pin is the barycenter, predict whether the orbit of Earth will be more elliptical or more circular.