Phases, Eclipses, and Tides

1. 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.

6. Motions of the Moon

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.

8. Phases of the Moon

11. What Causes 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.

12. The Cycle of the Phases • 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.

15. 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.

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

17. Solar Eclipses • 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.

18. Solar Eclipses

19. Total Solar Eclipses • 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.

20. Lunar Eclipses

21. Lunar Eclipses • 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.

22. Total Lunar Eclipses   • 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.

24. 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.