Spin! Day and Night
Adapted from Kinesthetic Astronomy, by Dr. Cherilynn A. Morrow and Michael Zawaski, 10 August 2004.
The Moon is the reason for our 24-hour day! In this 45-minute activity, children ages 10 to 13 explore Earth's rotation and the Moon's role. In part A, children use their bodies to model the Earth's daily motions in this kinesthetic exploration. The motion of the Earth about its axis (rotation) is related to the appearance of the sky over the course of the day. In part B, children consider the role of the Moon in slowing Earth's rotation over time; if the Moon didn't exist, Earth might be spinning more quickly, giving us an eight-hour day!
Note that this activity is appropriate for older children (ages 10 to 13) who are able to explore the geometry of Sun-Earth-Moon relationships in three dimensions. Many children under 10 are not able to fully conceptualize the Earth's spherical nature and their relationship to it, and so they are unable to create an accurate mental model.
What's the Point?
- Earth spins (rotates) once on its axis every 24 hours.
- The Sun appears to move across the sky in the same way every day, rising in the East and setting in the West.
- The Moon's gravitational pull on Earth influences Earth's motions. Over time, it has slowed Earth's spin from six hours to 24.
- Without the Moon's gravitational pull, Earth would be a very different place. Earth would probably spin more quickly, turning around once every eight hours. The faster spin would lead to faster winds, which would influence weather and ocean waves.
- Models — such as the children are creating here with their bodies — can be tools for understanding the natural world.
- An indoor or outdoor space large enough for the children to form a circle with arms outstretched to their sides
For the group:
- 1 (55"-wide) giant pumpkin or Halloween orange pumpkin garbage bag
- 1 (1/2"-wide) small grape or large blueberry
- 1 Earth globe
- 1 wearable sign depicting the Earth's continents, constructed using:
- Earth's Continents, printed preferably in color
- 2 (1'-long) strings or yarn
- Optional: Constellations of the Zodiac (adapted from Microsoft Office Clip Art and Media gallery images), printed preferably in color)
- Optional: Computer and projector to display an animation of Earth spinning
- Art supplies such as colored pencils, crayons, and markers
For each child:
- 2 directional signs, constructed using
- "East" and "West" sign template
- 2 popsicle sticks or pencils for handles
- 1 circle- or star-shaped sticker
- Without the Moon... 2 comic panel
- His/her Marvel Moon comic book and binder clip
For the facilitator:
- Background information
- Shopping list
- Review the background information.
- Provide an indoor or outdoor space large enough for the children to form a circle around the pumpkin. They must be able to stand with their arms outstretched and not touching. The experience will be most effective with at least eight children participating.
- Print, and if desired, laminate the Earth's Continents. Punch a hole in each of the upper ("northern") corners. Suspend the two pages from the strings to create a wearable sign.
- Print the "East" and "West" signs and tape the popsicle sticks or pencils to their backs.
- If possible, hang the constellation signs in order around the room in a counterclockwise direction.
- Set the pumpkin "Sun" on an elevated surface, such as a table, so that it is about the height of a child's navel.
- Optional: Set up a computer and projector for viewing the animation.
Facilitator's Note: While the Moon and Earth do not physically touch, they are linked by an invisible, but important, force: gravity. The Moon's gravity plays an important role in how the Earth moves — they are linked in an eternal "dance."
Part A: Earth Spins Once in a 24-hour Day
1. Explain to the children that they will use their bodies to model how Earth's spin — rotation — creates the cycle of day and night. Because the Moon and Earth are in motion together as they orbit the Sun, this model will be similar to a dance. Invite the children to form a circle around the "Sun" pumpkin. Explain that each child's upper body represents planet Earth. Ask the children to make sure they stand with enough room between each other to spread their arms out at shoulder height.
- What’s a model?
We use models to help us represent objects and systems so that we can study and understand them more easily. Scientists use computers to create models to study the complex interactions between the Sun, Earth, and Moon.
- Is your body — Earth — the appropriate size compared to the pumpkin — the Sun? No, it is too large.
- Remind the children of the scale model they created in Earth's Bright Neighbor and show them the grape or blueberry. How far would a grape- or blueberry-sized Earth really be from a pumpkin-sized Sun? About 491 feet or 150 meters (about three blocks).
- How far away do the children think the closest stars are in this model?
Alpha Centauri, the Sun’s nearest stellar neighbor, wouldn’t even be in the same country! It would be a pumpkin-sized star 25,000 miles away — a distance equal to the circumference of the real Earth at the equator!
2. Invite the children to become familiar with their Earth models by touching various geographic landmarks.
- Where is your North Pole? Top of the head.
- Where is your South Pole? At the bottom of the backbone (the tailbone).
- Where is the equator? It is an imaginary line drawn where the chest meets the belly and all the way around the belly.
- What hemisphere is above the equator? Northern.
- What hemisphere is below the equator? Southern.
- Where is North America? On our chests.
Distribute a sticker to each child and have everyone place them in the center of their chests (right over the breast bone/sternum). Explain that, for this model, the sticker represents "home."
- South America? Lower left belly.
- What is on the other side of Earth from North America? China and Asia.
- Where is Australia? Lower right back — "Down Under."
3. Distribute the "East" and "West" signs and invite the children to locate the cardinal directions. Place the globe at a child's belly with the U.S. facing outward and ask the children to look at their own bellies and determine which had should hold which sign. Allow them sufficient time to experiment and determine the directions with help from their neighbors.
- Which of your hands is eastward (towards New York on the U.S. map)?
- Which is westward (towards California on the U.S. map)?
Remind the children that North America is on their chests and use the globe to help them visualize the directions. Allow them to locate East and West and hold the signs in the appropriate hands: The right hand holds a "West" sign and the left hand holds an "East" sign.
4. Encourage caution as you have the children demonstrate the spin (rotation) of Earth. Have the children make the appropriate motions with their bodies as they answer the questions below. Physical motion is an essential tool for experiencing the day/night cycle of the Earth. Ask them to locate "home" on their bodies and remember to keep their heads in line with their bodies as they spin.
- How does the Sun appear to move in the sky? Rises in the east and sets in the west.
- What time of day is it at "home" when you face the Sun? Noon or midday. Why? The Sun is midway between east and west.
- What time of day is it when you face away from the Sun? Midnight. What do you see? Stars.
- What time of day is it along your backbone? Noon. What would people there see in the sky? The Sun.
- How many hours are between your front and back? Twelve.
- Where do you need to stand so that it is sunset at “home”? With the Sun just visible in front of the right arm and the "west" sign. What time is it on “home”? The sun sets earlier in winter and later in summer, but an in-between time is 6 p.m.
- What direction does the Earth spin so that the Sun appears to set in the west and rise in the east (i.e. re-appear in front of their outstretched "East" (left) hand as they continue to turn)? To the left, or counterclockwise.
- How long does it take Earth to spin once around its axis? 24 hours or 1 day.
5. Have the children "dance" like the Earth and observe the changing view of the sky from "home."
- Turn so that it is sunset at "home". What do you see in your sky? The Sun is near the right-hand horizon, low in the west. Do you ever see the Moon during this time of day? Yes.
- Turn so that it is midnight at "home". What do you see in your sky? Constellations. Do you ever see the Moon during this time of night? Yes.
- Turn so that it is sunrise at "home". What do you see in your sky? The Sun is near the left-hand horizon, low in the east. Do you ever see the Moon during this time of day? The group may have conflicting answers.
Explain that the Moon is sometimes visible in the morning sky and encourage them to look for it the next time they are up early.
- Turn so that it is noon at "home." What do you see in your sky? The Sun is high in the sky. Do you ever see the Moon during this time of day? The group may have conflicting answers.
If the children have not noticed the daytime Moon before, challenge them to look for it over the course of a month!
- What would happen to your dance if someone started pulling on your shirt? We wouldn’t be able to spin as quickly.
Explain that the Moon's gravity (and to a lesser extent, the distant Sun's gravity) acts much like someone pulling on their shirts: it pulls on the Earth's oceans (and on the less movable solid surface). The Moon’s pull is slowing us down.
Facilitator’s Note: How do we know that the Earth has been slowing down? Scientists count growth rings in coral fossils and ancient bacterial mounds, called stromatolites, like tree rings. Corals living 400 million years ago and bacteria living 3 billion years ago lived in a faster-paced world with shorter days and nights. Computer models trace the Moon's and Earth's motions backward in time. According to these models, the infant Earth had a six-hour day. With only the weaker pull of the Sun to slow it down, a Moon-less Earth might have an eight-hour day.
Part B: What If There Was No Moon?
6. Have the children consider what Earth's day and night cycle would be like if there was no Moon to slow its early, rapid spin. Ask them to spin quickly — and carefully! — to model an eight-hour day.
- What it would be like to go to sleep for only a four-hour night? How would they like to get ready for school every eight hours instead of every twelve?
- Scientists measure the solar system's fastest winds on the quickest planetary spinners: the giant planets Jupiter, Saturn, Uranus, and Neptune. What would our weather would be like on a rapidly spinning Earth? Winds would be faster.
- Ocean waves are caused by wind. What would surfing be like on a Moon-less Earth? Higher winds would cause higher waves, and there might be excellent surfing on a Moon-less Earth!
Regroup the children and discuss Earth's day and night cycle — and how different it would be without the Moon's gravitational pull to slow down its spin! If desired, reinforce the children's conceptions of Earth's day and night by viewing the animation of Earth spinning. Note that the movie has been "sped up" to show three days.
Scientists puzzle over whether the Moon-forming impact helped speed up the spin of the infant Earth, but it is certain that since then, the Moon has shaped our Earth's day and night cycle into its familiar 24-hour pattern! Scientists use computer models to help them understand the relationship between the Sun, Earth and Moon — just like the children used their own bodies!
Provide the children with their Without the Moon... 2 comic panels and art supplies. Allow them time to illustrate how different it would be on Earth with shorter days and shorter nights. Encourage creativity! Instruct them to add the panel as the next page in the Marvel Moon comic book by clipping the book together at the upper left corner.
Ask 10-year-old children to put their science skills to the test in the activity Moon Mythbusters. Invite children 11 and older to return for the next activity, Steady Partner, Steady Seasons, to explore the Moon’s role in providing Earth's long history of stable seasons.