Unit 10 – Space 2

1. Unit 10 – Space 2 Earth—Moon System Moon’s Rotation and Revolution Phases of the Moon Solar Eclipses Lunar Eclipses Moon Origin Theory Ocean Tides and the Moon

2. TAKS Practice – Space 2 • About how long does it take the Moon to complete the cycle shown above?(a) 1 day (b) 1 month (c) 1 year • Which phase of the Moon shown above does not reflect any sunlight towards Earth? (a) 1 (b) 2 (c) 3 (d) 4 • At which phase could a solar eclipse occur?(a) 1 (b) 2 (c) 3 (d) 4

3. TAKS Practice – Space 2 • About how long does it take the Moon to complete the cycle shown above?(a) 1 day (b) 1 month (c) 1 year • Which phase of the Moon shown above does not reflect any sunlight towards Earth? (a) 1 (b) 2 (c) 3 (d) 4 • At which phase could a solar eclipse occur?(a) 1 (b) 2 (c) 3 (d) 4

4. TAKS Practice – Space 2 • About how long does it take the Moon to complete the cycle shown above?(a) 1 day (b) 1 month (c) 1 year • Which phase of the Moon shown above does not reflect any sunlight towards Earth? (a) 1 (b) 2 (c) 3 (d) 4 • At which phase could a solar eclipse occur?(a) 1 (b) 2 (c) 3 (d) 4

5. TAKS Practice – Space 2 • About how long does it take the Moon to complete the cycle shown above?(a) 1 day (b) 1 month (c) 1 year • Which phase of the Moon shown above does not reflect any sunlight towards Earth? (a) 1 (b) 2 (c) 3 (d) 4 • At which phase could a solar eclipse occur?(a) 1 (b) 2 (c) 3 (d) 4

6. Guiding Questions – Space 2 • What are the rotation and revolution periods of the Moon? (p.646) • What causes the Moon to shine? (p.647) • What are the phases of the Moon? (pp.647-48) • What causes solar eclipses? Where and how often do they occur? (p.649) • What causes lunar eclipses? (pp.650) • What is the current theory explaining the origin of the Moon? (p.653) • What causes the ocean tides on Earth? (p.533)

7. 1. What are the rotation and revolution periods of the Moon? • The Moon has exactly the same periods of rotation (one spin on its axis) and revolution (one orbit around Earth), 27.3 days. This means that the same side of the Moon is always facing Earth. • It is not a coincidence that the two periods are the same. The Moon developed a bulge facing the Earth when it first formed, because of the Earth’s strong gravitational pull, and that stronger pull on the side with the bulge locks that side into always facing Earth.

8. 1. Moon Rotation / Revolution (cont.)

9. 2. What causes the Moon to shine? • The moon does not actually give off any light of its own. It simply reflects the light of the Sun which shines on it back to Earth. This is why the moon has different phases. If the sun is behind the Moon, as seen from Earth, none of the Moon’s face pointing towards Earth it lit by the Sun, and the Moon appears dark.

10. 3. What are the phases of the Moon? • Moon phases are the sequence of different shapes that the Moon’s lighted face takes as it orbits around the Earth, as seen from Earth. The phase at any time of the cycle depends on the relative positions of the Earth, Sun and Moon. • It takes 29.5 days for the Moon to complete all of the phases and return to the same shape. The difference between the period of rotation, 27.3 days, and the Moon phase cycle of 29.5 days is the result of the Earth’s motion around the sun. It takes the Moon another 2.2 days to catch up with the Earth’s movement around the Sun.

11. 3. Moon Phases (cont.) • A New Moon occurs when the Moon is between the Earth and the Sun, so that the lighted face of the Moon is facing away from the Earth, and the dark unlighted side is facing earth. The New Moon rises and sets with the Sun, and cannot be seen because it is dark. • After the New Moon, the phases begin waxing. Waxing means that more of the lighted half of the Moon is seen each night. After 3.7 days, a thin crescent shaped sliver of the lighted Moon is visible. This is the Waxing Crescent phase.

12. 3. Moon Phases (cont.) • About 7.3 days after the New Moon began the Moon phase cycle, about half of the Moon facing Earth is lit. This is the First Quarter Phase. This phase rises about noon and sets about midnight. • About 11 days after the New Moon, about ¾ of the Moon’s face is lit (as seen from Earth). This is called the Waxing Gibbous phase.

13. 3. Moon Phases (cont.) • About 14.75 days after the cycle began, the entire face of the Moon is lighted. This is the Full Moon phase. A Full Moon rises at about 6pm and sets around 6am, the opposite of the Sun. • About 18.4 days after the cycle began, the Moon has entered the waning phases, becoming darker each day. The ¾ lit moon is called the Waning Gibbous phase.

14. 3. Moon Phases (cont.) • About 22 days after the cycle began, about half of the Moon is lighted. This is the Third Quarter phase. A Third Quarter Moon rises at about midnight and sets around noon. • About 25.7 days after the cycle began, a thin sliver of the lighted face is visible. This is called the Waning Crescent phase. • At 29.5 days after the cycle began, another New Moon starts a new cycle.

15. 3. Moon Phases (cont.)

16. 4. What causes solar eclipses? Where and how often do they occur? • A Solar Eclipse occurs when the Moon moves directly between the Earth and the Sun, and casts its shadow over part of the Earth. Solar eclipses can either be total (the entire sun is blocked), partial (only part of the Sun blocked) or annular (the middle is blocked, leaving a ring of light).

17. 4. Solar Eclipses (cont.) • As seen from this location, the entire event takes about 2 hours. The Sun is only completely eclipsed for about 1 minute, and then slowly uncovered over an hour. This is a time lapse multiple exposure photo showing the entire 2002 solar eclipse in Africa.

18. 4. Solar Eclipses (cont.) • Only a narrow band of Earth experiences a total eclipse at any one event (in the “Umbra”), but a large area on either side of the total eclipse band sees a partial solar eclipse (in the “Penumbra”), where only part of the Sun is blocked.

19. 4. Solar Eclipses (cont.) • The darkest shadow, where the total eclipse occurs, is called the umbra. The lighter shadow, where only a partial eclipse occurs, is called the penumbra.

20. 4. Solar Eclipses (cont.) • Eclipses follow a 18 year, 11.3 day cycle called the Saros Cycle. This map shows the current cycle.

21. 5. What causes lunar eclipses? • When the Earth’s shadow falls on the Moon, a lunar eclipse occurs. Lunar eclipses can be total or partial. During a total lunar eclipse, light reflected off of Earth makes the Moon turn red when direct sunlight to the Moon is blocked.

22. 5. Lunar Eclipses (cont.) • The much larger umbra cast by Earth allows the entire night hemisphere of Earth to see a total lunar eclipse, provided the sky is clear.

23. 6. What is the current theory explaining the origin of the Moon? • Prior to the Apollo space missions, there had been three different theories about the Moon’s origin: the capture theory, the condensing theory, and the ejection theory. The Apollo missions uncovered evidence of a fourth theory, now most widely accepted, called the Impact Theory. Under this theory, a Mars-sized object collided with Earth, and caused a large part of Earth to be ejected into orbit around Earth, where it reformed into the Moon.

24. 6. Lunar Origin Theory (cont.)

25. 7. What causes the ocean tides on Earth? • Tides are caused by gravitational attraction between the Earth, Moon, and Sun. The Moon exerts a stronger pull on Earth than does the Sun. Water in the oceans bulges toward the Moon, and thus causes a high tide on the sides of Earth facing towards and away from the Moon. • When the Moon and Sun are on opposite sides of Earth from one another, the tides are highest. These are called Spring Tides. • Neap Tides occur when the Sun and Moon are at right angles to one another. They are lower.

26. 7. Ocean Tides (cont.)