Chapter 1 Earth, Moon, and Sun

1. Chapter 1Earth, Moon, and Sun Section 3 Phases, Eclipses, and Tides

2. Phases, Eclipses, and Tides • As the moon revolves around Earth and Earth revolves around the sun, the relative positions of all of them change. • These positions cause the phases of the moon, eclipses, and tides.

3. Motions of the Moon • The moon's orbit around Earth is an oval shape. • The moon rotates slowly on its own axis once every 27.3 days. • Because it revolves around Earth every 27.3 days, a “day” and a “year” on the moon are the same length. • The same side of the moon, the “near side,” always faces Earth. • The “far side” of the moon always faces away from Earth, so you never see it from Earth.

7. Phases of the Moon • The moon does not produce the light you see. It reflects light from the sun. • The different shapes of the moon you see from Earth are called phases. • The moon goes through all the phases each time it revolves around Earth…about once a month.

10. What Causes the Phases? • Phases are caused by changes in the relative positions of the moon, Earth, and the sun. • The sun lights the moon. • The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth.

11. Cycles of the Moon • During the new moon, the side of the moon facing Earth is not lit. • As the moon revolves around Earth, you see more and more of the lighted side of the moon every day, until the side of the moon you see is fully lit. • About 29.5 days after the last new moon, the cycle is complete, and you see a new moon again.

13. Eclipses • In most months the moon revolves completely around Earth without the moon moving into Earth's shadow or the moon's shadow hitting Earth. • When the moon's shadow hits Earth or Earth's shadow hits the moon, an eclipse occurs. • An eclipse occurs when an object in space comes between the sun and a third object, and casts a shadow on that object. • There are two types of eclipses: solar eclipses and lunar eclipses

14. Tilt of the Moon • The moon's orbit is tilted with respect to Earth's orbit. • So the moon rarely goes directly between Earth and the sun.

15. Solar Eclipse • A solar eclipse occurs when the moon passes between Earth and the sun, blocking the sunlight from reaching Earth. • The moon's shadow then hits Earth.

17. Total Solar Eclipse • The darkest part of the moon's shadow, the umbra, is cone-shaped. • From any point in the umbra, light from the sun is completely blocked by the moon. • The moon's umbra happens to be long enough so that the point of the cone can just reach a small part of Earth's surface.

18. Lunar Eclipse • A lunar eclipse occurs at a full moon when Earth is directly between the moon and the sun. • During a lunar eclipse, Earth blocks sunlight from reaching the moon. • The moon is then in Earth's shadow and looks dark from Earth. • Because the moon is closest to Earth's shadow during the full moon, lunar eclipses occur only at full moon

19. Lunar Eclipse

20. Total Lunar Eclipse • When the moon is in Earth's umbra, you see a total lunar eclipse. • You can see Earth's shadow on the moon before and after the total part of a lunar eclipse. • Unlike a solar eclipse, a lunar eclipse can be seen anywhere on Earth that the moon is visible.

21. Tides • Tides, the rise and fall of water, every 12.5 hours or so. • The force of gravity pulls the moon and Earth (including the water on Earth's surface) toward each other. • As Earth rotates, the moon's gravity pulls water toward the point on Earth's surface closest to the moon.

22. Tides • When the gravity of the moon and the sun pull from the same direction (new moon or full moon) it is called a spring tide and cause big differences between high tide and low tide levels. • When the sun’s pull and the moon’s pull meet at a right angle (first-quarter moon and third-quarter moon) it is called a neap tide, which have less noticeable high tides and low tides.

24. Study Guide • Section 3 • Phases of the moon (8) • Near side/ far side of the moon • Sunlight reflects off of the moon to make the phases • Solar eclipse • Lunar eclipse • Umbra • Tides • Spring tide/ Neap tide • Moon’s gravity causes the tides • Section 1 • Axis tilt • Seasons (equinoxes and solstices) • Rotation/revolution • Orbit • Section 2 • Gravity • Newton’s law of universal gravitation • Two factors: mass and distance • Weight changes due to gravity changes • Inertia • Newton’s first law of motion • Earth is in orbit because of two factors: gravity and inertia