from the "Moon" takes one large step toward the Moon.
- Why did the oceans move toward the Moon? The Moon's gravity pulled on them.
- What happened to the oceans? They moved apart around the "Earth" to form an oval rather than a circle shape.
Explain that the water from the oceans has "piled up" under the Moon and directly opposite the Moon. The two children standing beside "Earth" represent parts of the ocean where there is less water.
- Where are the oceans at the highest levels? The "oceans" nearest and furthest from the “Moon.” Are the coastal areas next to those “oceans” seeing a high or low tide? High.
- How many sides of the Earth experience high tide at the same time? Two (in general). Which part of "solid Earth" is experiencing high tide right now? The part that is under the "piled up" oceans.
- Where is low tide? Near the "oceans" standing closest to "Earth."
Note which body parts — the arms or front and back — are experiencing “high tide” and which are experiencing “low tide.”
- Why did the “ocean” furthest from the Moon move the least? It was “left behind.”
Facilitator's Note: The formation of the second ocean bulge is simplified in this model and ignores subtle motions of the Earth. A more accurate and complete description is presented in the following sources. Note that the science content level of these sources is intended for an adult audience.
"Our Restless Tides," National Oceanographic and Atmospheric Administration (NOAA)
Bad Astronomy: Misconceptions and Misuses Revealed, from Astrology to the Moon Landing "Hoax"
Philip Plait, John Wiley & Sons, Inc., 2002, ISBN 0471409766
Explain that the model demonstrates how the Moon produces two high tides and two low tides at the same time. The ocean furthest from the Moon is far enough away that it "feels less" of the Moon's gravitational pull.
- Is the solid Earth standing still, like in this model? No, it's spinning.
Invite "solid Earth" to spin about once on his or her axis (the line straight up from the floor to his or her head) a few times to demonstrate 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 h