Chapter 11

1. Chapter 11 Section 2 Phases, Eclipses, and Tides

2. I. Big Ideas • What causes the phases of the moon? • What causes solar and lunar eclipses? • What causes the tides?

3. II. Motions of the Moon • Earth’s closest neighbor in space is the moon • Average distance from Earth to the moon is only 30 times Earth’s diameter • On average Moon is 384,400 km from Earth

4. Moon revolves around Earth and Earth revolves around sun • The positions of the moon, Earth, and the sun cause the phases of the moon, eclipses, and tides

5. Moon revolves around Earth and rotates on its own axis • Moon’s orbit is a flattened circle or oval shape

6. Takes moon 27.3 days to revolve around Earth • Moon rotates slowly on its own axis once every 27.3 days • Because moon also revolves around Earth every 27.3 days – a “day” and a “year” on the moon are the same length

7. How many days does it take the moon to revolve once around the Earth?

8. III. Phases of the Moon • Moon reflects light from the sun • The moon does not produce its own light. • The different shapes of the moon you see from Earth are known as phases • The moon revolves around Earth about once a month.

9. 1. What causes phases? • Phases are caused by changes in the relative positions of the moon, Earth, and the sun. • Since moon revolves around Earth, you see moon from different angles • The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth

10. During the new moon, the side of the moon facing Earth is not lit • As moon revolves around Earth, you see more and more of lighted side until side of moon is fully lit • About 29.5 days after the new moon, the cycle is complete and you see new moon again.

11. Since moon does not produce light, how can you see it?

13. 2. Cycle of the Phases • New Moon • Sun lights side of moon facing away from Earth • Side facing Earth is completely dark • Waxing Crescent • See more and more of the lighted side of the moon

14. First Quarter • See half of the lighted side of the moon • Waxing Gibbous • Moon continues to wax (show more and more of the surface)

15. Full Moon • See the whole lighted side of the moon • Waning Gibbous • Fraction of lighted side of moon you see gets smaller each day

16. Third Quarter • Can see half of the moon’s lighted side Waning Crescent • See a crescent again

17. Turn to page 648 • Use a compass and create a graphic visual of the phases of the moon • Be sure to give your diagram a title • Don’t forget to label each phase

18. III. Eclipses • The moon’s orbit around Earth is slightly tilted with respect to Earth’s orbit around the sun • Due to this tilt the moon usually revolves completely around the Earth without the moon moving into Earth’s shadow or the moon’s shadow hitting Earth

19. When the moon’s shadow hits Earth or Earth’s shadow hits the moon, an eclipse occurs. • Eclipse = when an object in space comes between the sun and a third object, and casts a shadow on that object • Two types of eclipses: • Solar eclipse • Lunar eclipse Solar eclipse Lunar eclipse

20. IV. Solar Eclipses • During a new moon the moon is almost exactly between Earth and the sun. • However, most months the moon travels a little above or below the sun in the sky.

21. Solar eclipse occurs when the moon passes between Earth and sun, blocking the sunlight from reaching the Earth.

22. 1. Total Solar Eclipses • Umbra – the darkest part of the moon’s shadow; is cone shaped • From any point in the umbra, light from the sun is completely blocked by the moon

23. Only the people within the umbra experience a total solar eclipse • During a solar eclipse you can see the stars and the solar corona

24. 2. Partial Solar Eclipses • Penumbra – larger part of the shadow, part of the sun is visible from Earth • People in penumbra see only a partial eclipse • Not safe to look directly at the sun

25. V. Lunar Eclipse • During most months the moon goes near Earth’s shadow but not quite into it • Lunar eclipse – occurs at a full moon when Earth is directly between moon and sun • Earth blocks sunlight from reaching the moon – moon is then in Erath’s shadow and looks dark from Earth • Lunar eclipses occur only at full moon

27. 1. Total Lunar Eclipse • Earth’s shadow also has an umbra and penumbra • When moon is in Erath’s umbra, you see a total lunar eclipse

28. Lunar eclipse can be seen anywhere on Earth that the moon is visible • More likely to see total lunar eclipse than total solar eclipse

29. 2. Partial Lunar Eclipse • For most lunar eclipses Earth, moon, and sun are not quite in line • Partial lunar eclipse • Occurs when moon passes partly into umbra of Earth’s shadow

30. Why do lunar eclipses occur only at full moon?

31. VI. Tides • Tides = rise and fall of water • Water rises for about 6 hours, then falls for about six hours – generally takes 12.5 hours

32. Force of gravity pulls moon and Earth (including water on Erath’s surface) toward each other • Force of gravity between two objects depends on masses of objects and distance between them.

33. Tides occur mainly because of differences in how much the moon pulls on different parts of Earth. • As Earth rotates, moon’s gravity pulls water toward point on Erath’s surface closest to moon

34. Two high tides occur because of difference in force of gravity between one place and another • Two low tides on Earth located halfway between high tides

35. Height and timing of tides can vary • Not every place on Earth has two regular tides every day • Shapes of bays, inlets and ocean floor can affect flow of water