1. Earth and Space Science
Earth and Sun

2. gravity
1. The force of attraction, or pull, between two objects is called ______________.

3. mass, distance, decreases
2. The strength of the pull of gravity is affected by the total ___________ of the two objects and by the _____________ between them. The pull of gravity _______________ when the total mass of the two objects decreases and when the objects are farther apart.

4. greater
3. The Sun’s gravitational pull on Earth is ________________ than its pull on a planet much farther away, such as Neptune.

5. Sun
4. The planets are held in their orbits around the _________ by the force of gravity between each planet and the Sun.

6. orbit
5. A path that one object takes as it moves around another object is its ________________.

7. inertia
6. Gravity is not the only force acting on a planet. _______________ is the tendency of a moving object to keep moving in a straight line. Gravity and inertia work together to keep the planets moving in their orbits.

8. ellipse
7. Earth moves in a nearly circular orbit shaped like an _____________.

9. 365 , revolution
8. Every year, or ____________ days, Earth makes one complete trip, or ______________, around the Sun.

10. seasons, angles
9. During a year, you observe ____________ changing on Earth. Seasons occur because as Earth revolves around the Sun, sunlight strikes different parts of Earth at different ___________.

11. axis
10. Earth’s axis is tilted about 23˚. An __________ is a straight line about which an object spins.

12. winter, summer
11 When the Northern Hemisphere is tilted away from the Sun, the season there is ___________. When it is winter in the Northern Hemisphere, it is _______________ in the Southern Hemisphere.

13. opposite
12. Because the tilt of Earth’s axis always points in the same direction, the season in the Northern and Southern Hemisphere are always _____________________.

14. rotation, 24
13. In addition to Earth revolving around the Sun, it is also spinning. One ________________ is a complete spin on the axis. Earth makes one rotation every day or _______ hours.

15. daylight, darkness
14. At any point in time, half of Earth faces the Sun and is in ______________ . The other half of Earth’s surface faces away from the Sun and is in __________.

16. summer, shorter
15. The tilt of Earth’s axis affects the length of the day. There are more daylight hours during ____________ and during winter, the amount of daylight is __________.