1. Ch. 23 The Sun-Earth-Moon System
Earth Science

2. Section 1 – Earth Learning Objectives
Examine Earth’s physical characteristics.
Differentiate between rotation and revolution.
Discuss what causes seasons to change.

3. Section 1 – Earth
A. Properties of Earth – people used to think that Earth was flat and at the center of the universe.
1. Earth is now known to be a round, three- dimensional sphere.

4. a. Axis – imaginary vertical line around which Earth spins
b. Rotation – the spinning of Earth around its axis that causes day and night

5. 2. Earth has a magnetic field with north and south poles.
Add to notes  thought to be generated by Earth’s outer core, made of liquid iron.

7. 3. Magnetic axis – imaginary line joining Earth’s magnetic poles
a. Earth’s magnetic axis does NOT align with its rotational axis.
b. The location of magnetic poles slowly changes over time.

9. B. Causes of seasons
1. Revolution – Earth’s yearly orbit around the Sun
a. Earth’s orbit is an ellipse, or elongated, closed curve.
b. Because the Sun is not centered in the ellipse, the distance between Earth and the Sun changes during the year.

10. 2. Earth’s tilt causes seasons.
a. The hemisphere tilted toward the Sun receives more daylight hours than the hemisphere tilted away from the Sun.
b. The longer period of sunlight is one reason summer is warmer than winter.

12. 3. Earth’s tilt causes the Sun’s radiation to strike the hemispheres at different angles.
a. The hemisphere tilted toward the Sun receives more total solar radiation than the hemisphere tilted away from the Sun.
b. In the hemisphere tilted toward the Sun, the Sun appears high in the sky and the radiation strikes Earth more directly.

13. C. Solstice – the day when the Sun reaches its greatest distance north and south of the equator.
1. Summer solstice occurs June 21 or 22 in the northern hemisphere
2. Winter solstice occurs December 21 or 22 in the northern hemisphere.

15. D. Equinox – the day when the Sun is directly over Earth’s equator
1. Daylight and nighttime hours are equal all over the world.
2. Spring equinox occurs on March 20 or 21 in the northern hemisphere.
3. Fall equinox occurs on September 22 or 23 in the northern hemisphere.

17. Discussion Question
Why do the southern and northern hemispheres experience opposite seasons?

18. Discussion Question
Why do the southern and northern hemispheres experience opposite seasons?
 Due to Earth’s tilt on it’s axis, the surface that is exposed to the Sun changes as Earth revolves around the Sun.

19. Section 2 – The Moon – Earth’s Satellite
Learning Objectives
Identify phases of the Moon and their cause.
Explain why solar and lunar eclipses occur.
Infer what the Moon’s surface features may reveal about its history.

20. Section 2 – The Moon – Earth’s Satellite
A. Motions of the Moon
1. The Moon rotates on its axis.
2. The Moon’s rotation takes 27.3 days with the same side always facing Earth. (rotation = revolution)
3. The Moon seems to
shine because it reflects
sunlight.

21. B. Moon phases – the different forms the Moon takes in its appearance from Earth.
1. New moon – when the Moon is between Earth and the Sun and cannot be seen.

22. 2. Waxing phases – more of the illuminated half of the Moon that can be seen each night after the new moon.
a. First visible thin slice of the moon is a waxing crescent.
b. First quarter phase – half the lighted side of the Moon is visible.
c. Waxing gibbous – more than one quarter is visible.
d. All of the Moon’s lighted side is visible during a full moon.

24. 3. Waning phases – less of the illuminated half of the Moon is visible after the full moon.
a. Waning gibbous – starts after a full moon when more than half of the lighted side is still visible.
b. Only half the Moon’s lighted side is visible during the third quarter phase.
c. The last visible slice before a new moon is called the waning crescent.

27. 4. The Moon completes its cycle of phases in about 29
4. The Moon completes its cycle of phases in about days instead of 27.3 days because it is keeping up with Earth’s revolution around the Sun.

28. C. Eclipses – when the Earth or Moon casts a shadow on the other.
Solar eclipse – the Moon moves directly between Earth and the Sun, shadowing part of Earth.

29. a. Under the umbra, or darkest part of the shadow, a total solar eclipse occurs.
b. A partial solar eclipse happens in the lighter shadow on Earth’s surface called the penumbra.
c. A total solar eclipse is visible only on a small area of Earth.

30. 2. Lunar eclipse – when Earth’s shadow falls on the Moon.
a. If the Moon is completely in Earth’s umbra, a total lunar eclipse occurs.

31. b. Partial lunar eclipse – when only part of the Moon moves into Earth’s umbra, or the moon is totally in the penumbra.
c. A total lunar eclipse is visible on the nighttime side of the Earth when the night is clear.

32. Add to notes  A solar eclipse is more rare to see than a lunar eclipse.

33. D. The Moon’s surface has many depressions, or craters, formed from meteorites, asteroids, and comets.
1. Cracks in the Moon’s crust caused lava to fill large craters, forming maria, or dark, flat areas.
2. Igneous maria rocks are 3 to 4 billion years old, indicating craters formed after the surface cooled.

36. E. Data from moonquakes suggest that under the Moon’s crust might lie a solid mantle, then a partly molten mantle and a solid, iron-rich core.

37. Add to notes: 2 other theories…
F. Impact theory of Moon origin – the Moon formed 4.6 billion years ago from Earth material thrown off when a large object collided with Earth.
Add to notes: 2 other theories…
Moon was captured by Earth’s gravity
Moon and Earth condensed from the same cloud of dust and gas

38. Discussion Question
Why is there approximately a two-day difference between the lunar cycle of phases and the lunar revolution around Earth?

39. Discussion Question
Why is there approximately a two-day difference between the lunar cycle of phases and the lunar revolution around Earth?
 As the Moon revolves around Earth, Earth is revolving around the Sun at the same time. It takes two extra days for the Moon to keep up with Earth as it orbits the Sun.

40. Section 3 – Exploring Earth’s Moon
Learning Objectives
Describe recent discoveries about the Moon.
Examine facts about the Moon that might influence future space travel.

41. Section 3 – Exploring Earth’s Moon
A. Missions to the Moon
1. Early exploration
a. The first Luna spacecraft, launched by the Soviet Union in 1959, enabled close study of the Moon.

43. b. The Ranger spacecraft and the Lunar Orbiters of the U. S
b. The Ranger spacecraft and the Lunar Orbiters of the U.S. took detailed photographs of the Moon in the 1960s.
c. Five Surveyor U.S. spacecrafts landed on the Moon.

44. d. Astronauts of Apollo 11 landed on the Moon in 1969.

45. 2. The Clementine spacecraft was placed in lunar orbit in 1994 to survey the moon’s surface.
a. Collected data on the mineral content of Moon rocks
b. Mapped features on the Moon’s surface

46. c. Impact basins, or craters, are depressions left by objects striking the Moon.
d. Identified South Pole-Aitken Basin, the largest and deepest impact crater in solar system.

47. B. Mapping the Moon
1. Data from Clementine yielded a map of the Moon showing its composition.
a. The Moon’s crust is thinnest under its impact basins.
b. The crust on the side of the Moon facing Earth is thinner than on the far side.

49. 2. The Lunar Prospector was launched in 1998 to look for clues about the Moon’s origin and makeup.
a. Small, iron-rich core of the Moon supports the impact theory of the Moon’s origin.
b. Findings confirmed that ice was present in deep craters at poles.

50. Discussion Question
Why is it important to know if there is water on the Moon (or any other planet)?

51. Discussion Question
Why is it important to know if there is water on the Moon (or any other planet)?
 Water is essential to support life and any humans in a Moon colony