Lesson 1 Reading Guide - KC

1. Earth’s Motion • How does Earth move? • Why is Earth warmer at the equator and colder at the poles? • Why do the seasons change as Earth moves around the Sun? Lesson 1 Reading Guide - KC

2. Earth’s Motion • orbit • revolution • rotation • rotation axis • solstice • equinox Lesson 1 Reading Guide - Vocab

3. Earth and the Sun • The nearest star to Earth is the Sun. • The Sun is approximately 150 million km from Earth. • The Sun’s diameter is more than 100 times greater than Earth’s diameter. • The Sun’s mass is more than 300,000 times greater than Earth’s mass. Lesson 1-1

4. Earth and the Sun(cont.) Earth moves around the Sun in a nearly circular path. Lesson 1-1

5. Earth and the Sun(cont.) • The path an object follows as it moves around another object is an orbit. • The motion of one object around another object is called revolution. • Earth makes one complete revolution around the Sun every 365.25 days. Lesson 1-1

6. Earth and the Sun(cont.) Earth orbits the Sun because the Sun’s gravity pulls on the Earth. Lesson 1-1

7. Why does the Earth orbit the Sun? • Think of the Earth like an object on a string being twirled around the Sun. • If the string (gravity) were to be cut, the Earth would fly off into space in a straight line.

8. Earth and the Sun(cont.) • A spinning motion is called rotation. • One complete rotation of Earth takes about 24 hours. Lesson 1-1

9. Earth and the Sun(cont.) • The line on which an object rotates is the rotation axis. • The tilt of Earth’s rotation axis is always in the same direction by the same amount. Lesson 1-1

10. What causes sunrises and sunsets? • Each day it appears the Sun moves from east to west across the sky • It seems as if the Sun is moving around the Earth, but it is not, the Earth rotates from west to east. So the Sun appears to move east to west.

11. Temperature and Latitude As the Earth orbits the Sun, only one half of Earth faces the Sun. Because Earth’s surface is curved, different parts of Earth’s surface receive different amounts of the Sun’s energy. Lesson 1-2

12. Temperature and Latitude(cont.) • Relative to the direction of a beam of sunlight, Earth’s surface tends to become more tilted as you move away from the equator. • At the equator the sunlight is less spread out • Above and below the equator the sunlight is more spread out Lesson 1-2

13. Temperature and Latitude(cont.) The energy in a beam of sunlight tends to become more spread out the farther you travel from the equator Lesson 1-2

14. Temperature and Latitude(cont.) Regions near the poles receive less energy than regions near the equator, which means Earth is colder at the poles and warmer at the equator. Lesson 1-2

15. Seasons During one half of Earth’s orbit, the north end of the rotation axis is toward the Sun. Lesson 1-3

16. Seasons(cont.) • Due to Earth’s tilt, the northern hemisphere receives more solar energy during half of Earth’s rotation. • Temperatures increase in the northern hemisphere and decrease in the southern hemisphere. • This is when spring and summer happen in the northern hemisphere, and fall and winter happen in the southern hemisphere. Lesson 1-3

17. During the other half of Earth’s orbit, the north end of the rotation axis is away from the Sun. Lesson 1-3

18. Seasons(cont.) • Due to Earth’s tilt, the southern hemisphere receives more solar energy during this half of Earth’s rotation. • Temperatures decrease in the northern hemisphere and increase in the southern hemisphere. • This is when fall and winter happen in the northern hemisphere, and spring and summer happen in the southern hemisphere. Lesson 1-3

19. Seasons(cont.) There are four days each year when the direction of Earth’s rotation axis is special relative to the Sun. Lesson 1-3

20. Seasons(cont.) A solsticeis a day when Earth’s rotation axis is the most toward or away from the Sun. Lesson 1-3

21. Seasons(cont.) An equinoxis a day when Earth’s rotation axis is leaning along Earth’s orbit, neither toward nor away from the Sun. Lesson 1-3

22. Seasons(cont.) The Sun’s apparent path through the sky in the northern hemisphere is lowest on the December solstice and highest on the June solstice. Lesson 1-3

23. The gravitational pull of the Sun causes Earth to revolve around the Sun in a near-circular orbit. Lesson 1 - VS

24. Earth’s rotation axis is tilted and always points in the same direction in space. Lesson 1 - VS

25. Equinoxes and solstices are days when the direction of Earth’s rotation axis relative to the Sun is special. Lesson 1 - VS

26. 18. Which body’s gravitational pull causes the Earth to orbit the Sun? A. Earth B. Sun C. Moon D. none of these Lesson 1 – LR1

27. 19. Relative to the direction of a beam of sunlight, what happens to Earth’s surface as you move away from the equator? A. The surface becomes less tilted. B. The surface becomes flat. C. The surface becomes more tilted. D. There is no change in the relationship. Lesson 1 – LR2

28. 20. Which term refers to the motion of one object around another object? A. orbit B. rotation C. rotation axis D. revolution Lesson 1 – LR3

29. 21. Earth’s movement around the Sun causes sunrises and sunsets. 22. Earth has seasons because its distance from the Sun changes throughout the year. Do you agree or disagree? Lesson 1 - Now