nstrate about one day. Explain that the Moon is also moving — orbiting around the Earth over about 27 days — and that the oceans are dragged along with the solid Earth as it spins. Have Earth stop spinning in a new position. Note again which body parts — the arms or front and back — are experiencing "high tide" and which are experiencing "low tide."
- Is high tide still near the same place (i.e. is "high tide" still near the arms or front and back), or is it in a new place? Is low tide still in the same place? No, high and low tide are on different parts of the solid Earth now.
Summarize that the Moon's gravitational pull creates two high and low tides for most coastal areas on Earth each day. As the Earth spins, the tide flows in and out.
Part B: What If There Was No Moon?
3. Ask the children to consider what Earth’s tides would be like if there was no Moon. Have the "oceans" stand in their original positions around the "Earth" so that the scarves or strips of fabric are linked in a circle. Have a new volunteer put on the yellow T-shirt and join the model as the "Sun." Invite "Moon" to rejoin the audience.
- Would the Earth still have tides? Accept all answers.
- Besides the Moon, what pulls on the Earth? The Sun.
- Does the Sun pull on Earth's oceans?
Explain that the Sun does pull on Earth and its oceans (and keeps them in orbit). Have the children to recall from the scale model that they constructed in Earth's Bright Neighbor that the "Sun" was a pumpkin 491 feet or 150 meters (about three blocks) from a grape- or blueberry-sized "Earth." Since it is so far away, the Sun's pull gives the tides only a third of their height.
- The "Moon" pulled the nearest "ocean" three steps forward. How many steps forward does the "Sun" alone pull him or her? One-third as many steps, or one step forward.
4. Have the children model how tides would be smaller on a Moon-less Earth with only the Sun to pull on the oceans. Have the child nearest the "Sun" take one large step toward him or her. “Earth” and the two standing beside him or her take one normal step toward the "Sun." The child furthest from the "Sun" takes one small step forward.
- What happened to the oceans? They moved apart around the "Earth," but the "oceans" nearest to and furthest from the "Sun" are still fairly close to "Earth."
- Can the children find two sides of "Earth" where there is high tide and low tide?
- How might the coastal areas change during a day with only the Sun creating tides? The difference between high and low tide would not be as extreme.
Facilitator's Note: The time of high tide changes each day because the Moon is moving around the Earth. If we had no Moon, the tide due to the Sun alone would occur at essentially the same time every day.
Regroup the children and discuss Earth’s tides — and how different it would be without the Moon's gravitational pull adding significantly to the height of the tides. Explain some of the effects of tides on marine life: Tides create tide pools along rocky shores and where many creatures breed, feed, and hunt. Other creatures thrive in places like harbors, bays, and mangroves where the tide exposes mud flats or tree roots. Tides create currents that mix the ocean, spreading nutrients and removing waste.
- Many people live far from the oceans. Why is the ocean important to everyone? The children may have many ideas. They may have heard how oceans cover most of Earth's surface (71%) and contains most of the planet's water (97%). They may have learned how oceans influence weather. Seafood — including types that live, hatch, breed, or hunt in areas exposed by tides — is available to people living inland.
- What would a Moon-less Earth would be like with smaller tides?
Allow the children time to illustrate the influence of smaller tides in their Without the Moon... 3 comic panels.
Studying the motions and gravitational pull of the Moon today helps scientists understand its influence on Earth today — and long ago. Scientists use computer models to help them understand the relationship between the Sun, Earth and Moon — just 