Tides

1. Tides • First a few clicker questions to introduce tides.

2. Goals & Outcomes • Appreciating science in general, and astronomy in specific. • Understanding how knowledge is gained and be critical of what you see and hear. You will begin to ask “How can we test that?” when forming hypotheses or “How do we know that?” when reading new information. • Developing a working knowledge of the scientific method and how to apply it to real world situations. • Critically analyzing and evaluating information, scientific or otherwise • Understand how tides, tidal stretching, and orbits are related to gravity.

3. Big questions • What causes tides? • What worlds do they affect? • How do they affect these worlds? • How are the tide-creators affected? • Give examples.

4. Original location B C A Earth Objects A, B, C are above the Earth, A at top, B middle, C bottom. They all start falling simultaneously. Which one experiences the largest acceleration due to Earth’s gravity? • A • B • C • All 3 are the same

5. Original location C B C A A B A C C C A B C A B B B A Which picture shows the spacing after a little while, when all objects are still falling? • 1 • 2 • 3 • 4 • 5 1 = Original spacing 2 3 4 5

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7. __________ forces Gravity _____________ ___________ as it falls. This is called ____, theyare _______________ __________________ Between the ________, _______________, and _______________. Technically there is no such thing as a “tidal force.” _____________ ___________________ ___________________. Neat info: The “tidal forces” are what kill you as you fall into a black hole. Good __________________ on p. 140.

8. Standing under the Moon, how does the Moon affect your weight here on Earth? • Increases your weight noticeably • Decreases your weigh noticeably • No noticeable change

9. More on tides ______________ (therefore) ____ work on: • _______________________ and • ________________________ Common misconception: many people think you need liquid on the surface to experience tides. But the _____________ _____________________________ too! • __________________________ because • land is ______________________.

10. Tides on worlds • Which objects do you think can cause noticeable tides on Earth? • On the Moon? • Mercury? • Venus? • Io? • Europa? • Titan? • Pluto? Pluto’s moon Charon?

11. Tidal Forces – ___ also _________

12. Tidal Forces – again, see also figure 4.23. And see also “common misconception” on page 141 With your neighbor, decide where water would be deep & shallow if we added a LOT of water to Earth.

13. Tidal Forces – still figure 4.23 How many high tides are there on Earth right now? How often are there high tides are there at the beach each day? Moon moves in its orbit, so that _____ _______________. The arrow in this picture shows the Moon to the left. Where else could the Moon be to have identical Earth tides?

14. Mixing Sun & Moon tides • When Sun & Moon tides work together: “spring tides.” See top of figure 4.25, page 141. • water “springs” upwards. • When Sun & Moon tides work against each other: “neap tides.” See bottom of figure 4.25. • neap: from Old English “nep” which means “to lower” • Here’s an Interactive figure 4.25 on your CD or on Mastering Astronomy

15. Tide table, part 1 – monthly cycle Note: Would you expect the 2 high tides each day to be the same strength? Are they? Why not? (Not answered in class.) Think three dimensionally!

16. Tide table, part 2 (one day)

17. Tidal Effects from Moon – see fig ____ • Tides cause the ____________, causing _____ __________________. (clicker) • Earth _____________________ (by ~ 2ms/century). • _____________ also causes ______________ • ____________________________________ • __________________ & now probably ___________ • See fig 4.26 for more detailed explanation. • Length of Earth’s day __________________ • Neat trivia: 100 million years ago: • Were days longer or shorter? • Does the orbit time change • 1 day was ____________ hrs long • ______ days in a year. Why _______ days?

18. Tides on the Moon • Just like Moon causes tides on the Earth, _______ causes tides on ___________. • Remember, tides are caused by • ___________________________ • Which object experiences a larger difference on its edges? (clicker)

19. Which object should cause larger land tides on the other? • Moon causing tides on the Earth • Earth causing tides on the Moon • Both should be equal

20. Tidal Effects on the Moon • ________ causes ____ to _________ • _________________________ until… • The __________________________. • __________________ (synchronized) • _______________________________. • Fancy words: The _________________ of the Moon is ______________________________________. See pages ___________.

21. A bit about _____________ moons • ____ • __________________ • _____________ • _______________________________ • _________& _______________________________? • All 4 are approximately the size of ___________ • Ganymede & Callisto are _____________________ • (_______________Earth’s size instead of_________) • All 4 are about the _______________________ • as _______________________________________

22. Do you think Jupiter’s moons are synchronized? • Yes • No

23. Synchronous rotation • Eventually _________________. In other words… • _________________________________ ___________________________: • Is our day getting longer or shorter? • Why hasn’t it synchronized yet? • The period of the Earth’s rotation (a.k.a. ___) • will = the time it takes the Moon to revolves around the Earth (a.k.a. __________) • Then, 1 ___________________________ =~___ current “_______” [How many days/yr?] • This won’t occur for ___________________

24. When the Earth is synchronized with the Moon, will the Moon show us different phases? • Yes • No

25. Another result of tidal friction As the _______________ due to ____________________ __________________________________________. • ______________________________________________. As Moon ______________________, what would we observe? • Moon ____________________________ • ______________________________________ • ___________________________________ As Moon ______________________, will its orbit time increase, decrease or stay the same? (no clicker) Were tides weaker, stronger, or the same in the past? [next clicker slide] Important for forming life! (water less stagnant)

26. Tides affecting other moons’ orbits • _____________ is ____________________________ • Orbits very close to Mars. What does that tell you? • Orbits once every _____________. Mars “day” = 24h 40 m • How does the tidal bulge on Earth affect Moon’s orbit? Why that way? • How does tidal bulge ON Mars affect Phobos’ orbit? • tides __________________ because it orbits more than once per day • Phobos will _________, more likely, _______________ in 50 million years (_________________) • ________________ is __________________ moon • Orbits _____. _____ things rotate & revolve ____________________ • Will also ________________________, in 100 million years.

27. 100 million years ago, Earth’s high tides were: • Stronger than they are now • Weaker than they are now • The same size as they are now

28. Summary of tides • What mechanism causes tides in general? • What objects cause tides here on Earth? • Name 2 other worlds that experience significant tides, and what are the tide sources? • How have tides affected the Moon’s appearance from Earth? • What is changing in the Earth-Moon system as a result of tides?