1. Sci. 2-1 A Solar System is born
Pages 34-42

2. Solar System- made of a sun (star) and the planets and other bodies that travel around it.
1) Our solar system has the sun, 8 planets, & an asteroid belt. Pluto is a dwarf planet.

3. B. The solar system formed out of a vast cloud of cold gas and dust called a nebula.

4. C. Particles move closer to each other because of gravity but bounce away from each other when they collide ( pressure). This movement keeps the nebula in balance.

5. D. Gravity and pressure were balanced, keeping the cloud unchanging until something upset the balance such as 2 nebulae crashing into each other, or a nearby star exploding causing material to crash into the cloud. Then the nebula began to collapse.

6. E. Collapse of the solar nebula caused heating in the center
E. Collapse of the solar nebula caused heating in the center. As material crowded closer together, planetesimals began to form. Planetesimals- bits of dust from the nebula sticking together.

8. F. The central mass of the nebula became the sun
F. The central mass of the nebula became the sun. Planets formed from the surrounding disk of materials ( planetesimals).

9. G. In the cooler, outer part of the solar nebula, the planets were able to collect large amounts of dust. Once they became large enough, their gravity attracted gases making the Gaseous Giant Planets.

10. H. Closer to the sun, it is too hot for gases to remain so the inner planets are made mostly of rocky material

11. I. It took about 10 million years for the solar system to form and it is now 4.6 billion years old.

12. J. Rotation- spinning on its axis. (24 hours = 1 day)

13. K. Orbit- the path Earth travels around the sun.

14. L. Revolution- 1 trip around the sun
M. Period of revolution- the time it takes to revolve once (365 days = 1 year)

15. N. Kepler discovered the planets do not move in circles around the sun
N. Kepler discovered the planets do not move in circles around the sun. They move in a elongated circle called an ellipse.

16. O. Astronomical Unit (AU)- the average distance between the earth and the Sun- 150 million Km.

17. P. Kepler’s 2nd Law- planets move faster in their orbits when they are closer to the sun.

18. Q. Kepler’s 3rd Law- by knowing a planet’s period of revolution , the planet’s distance from the sun can be calculated.

19. R. Gravity depends on the masses of the interacting objects and the distances between them.