1. Welcome to the Neighborhood Our Solar System

2. What’s the difference between rotation and revolution? Each planet spins on its axis. Each planet spins on its axis. This spinning is called rotation. This spinning is called rotation. Q: How long does it take the Earth to rotate on its axis once? Q: How long does it take the Earth to rotate on its axis once? A: Approximately every 24 hours. This is equal to one day. A: Approximately every 24 hours. This is equal to one day.

3. What’s the difference between rotation and revolution? Q: How much of the Earth is facing the sun at any time? Q: How much of the Earth is facing the sun at any time? A: Half of the Earth faces the sun A: Half of the Earth faces the sun Half of the Earth has day and the other has night. Half of the Earth has day and the other has night.

4. What’s the difference between rotation and revolution? Q: What is the path that one body follows as it travels around another body is space is called? Q: What is the path that one body follows as it travels around another body is space is called? A: Orbit A: Orbit One complete trip along an orbit is called a revolution. One complete trip along an orbit is called a revolution.

5. What’s the difference between rotation and revolution? Q: Do all planets in our solar system have the same period of revolution? Q: Do all planets in our solar system have the same period of revolution? A: No! A: No! Q: Which planet do you think has the shortest period of revolution? Longest? Q: Which planet do you think has the shortest period of revolution? Longest?

6. What’s the difference between rotation and revolution? Q: How long is Earth’s period of revolution (or the time it takes Earth to orbit or revolve around the sun once)? Q: How long is Earth’s period of revolution (or the time it takes Earth to orbit or revolve around the sun once)? A: One year = 365.25 days A: One year = 365.25 days How many revolutions have you made around the sun?

7. Review Rotation = the spin of a body on its axis Rotation = the spin of a body on its axis Orbit = the path that a body follows as it travels around another body in space Orbit = the path that a body follows as it travels around another body in space Revolution = the motion of a body that travels around another body in space; one complete trip along an orbit Revolution = the motion of a body that travels around another body in space; one complete trip along an orbit

8. Johannes Kepler (1571 – 1630) German astronomer German astronomer Influenced by the Copernicus Influenced by the Copernicus Professor of mathematics Professor of mathematics Contemporary of Galileo Contemporary of Galileo Described the orbit of Mars Described the orbit of Mars He wrote three laws that are important to astronomy and are known as Kepler’s Laws He wrote three laws that are important to astronomy and are known as Kepler’s Laws

9. Kepler’s Laws 1. Planets orbit the sun in an elongated circle called an ellipse 2. Planets move faster when they are closer to the sun, and slower when they are further away 3. Planets that are closer to the sun orbit faster than planets farther away

10. Sir Isaac Newton (1642 – 1727) Newton was born in England the same year Galileo died. Newton was born in England the same year Galileo died. He is the most influential scientist who ever lived He is the most influential scientist who ever lived He defined the laws of motion and universal gravitation which he used to predict precisely the motions of stars, and the planets around the sun. He defined the laws of motion and universal gravitation which he used to predict precisely the motions of stars, and the planets around the sun. Newton constructed the first reflecting telescope. Newton constructed the first reflecting telescope.

11. Universal Gravitation An objects are attracted to each other because of gravity An objects are attracted to each other because of gravity This attraction depends on the mass of the two objects and the distance between them This attraction depends on the mass of the two objects and the distance between them The larger the masses of the two objects and the closer they are to each other, the greater the force of gravity between them The larger the masses of the two objects and the closer they are to each other, the greater the force of gravity between them

12. Gravitational force is the dominant force the determining motions in the Solar System. Gravity keeps the planets in orbit around the sun.

13. If gravity pulls objects together, why doesn’t the moon come crashing into the Earth? If gravity pulls objects together, why doesn’t the moon come crashing into the Earth?

14. Orbits Falling Down and Around The moon has inertia. The moon has inertia. Newton's first law of motion states that "An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force." Newton's first law of motion states that "An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force." In other words, objects tend to "keep on doing what they're doing." In other words, objects tend to "keep on doing what they're doing." This tendency to resist changes in their state of motion is described as inertia. This tendency to resist changes in their state of motion is described as inertia.

15. Orbits Falling Down and Around Q: There is no air in space. What effect do you think this has on the moon’s inertia? Q: There is no air in space. What effect do you think this has on the moon’s inertia? A: No air = no resistance. The moon continues to move. A: No air = no resistance. The moon continues to move.

16. Orbits Falling Down and Around Q: But what about gravity? Q: But what about gravity? A: The combination of the moon’s inertia AND gravity is what causes the moon to move in a circular path around the Earth. A: The combination of the moon’s inertia AND gravity is what causes the moon to move in a circular path around the Earth. Q: Is this why we revolve around the Sun in an elliptical orbit? Q: Is this why we revolve around the Sun in an elliptical orbit? A: Yes! A: Yes!

17. Review

18. Kepler discovered that planets move faster when they... A) are farther from the sun. B) are closer to the sun. C) have more mass. D) rotate faster. Answer: B) Planets move faster when they are closer to the sun.

19. What is the difference between rotation and revolution? Rotation = the spin of a body on its axis Rotation = the spin of a body on its axis Revolution = the motion of a body that travels around another body in space; one complete trip along an orbit Revolution = the motion of a body that travels around another body in space; one complete trip along an orbit

20. What causes a day? The rotation of the Earth once on its axis. The rotation of the Earth once on its axis. It is approximately 24 hours. It is approximately 24 hours.

21. What causes a year? The revolution of the Earth once around the sun. The revolution of the Earth once around the sun. It is approximately 365.25 days. It is approximately 365.25 days.

22. On what two properties does the force of gravity between two objects depend? Mass (the amount of matter in an object) Mass (the amount of matter in an object) Distance (how far apart they are) Distance (how far apart they are)

23. What two properties cause an object to have an elliptical orbit? Inertia (an object in motion continues at the same speed and direction, unless acted upon by a force) Inertia (an object in motion continues at the same speed and direction, unless acted upon by a force) Gravity (the force that causes to objects to be pulled toward each other) Gravity (the force that causes to objects to be pulled toward each other)

24. Homework Use pages 630 – 633 in your text book to complete the Guided Reading for this section. Use pages 630 – 633 in your text book to complete the Guided Reading for this section. It is due tomorrow. It is due tomorrow.