Fruit Loops: Exploring our Moon's Phases and the Reason for Eclipses
An Activity from SkyTellers • Lunar and Planetary Institute
Children explore the dynamics of lunar phases and eclipses to develop an understanding of the relative positions of our Moon, Earth, and Sun that cause the phases of the Moon and eclipses viewed from Earth. The idea that the Moon does not produce its own light, but simply reflects the light of the Sun, is reinforced.
Invite the children to share what they have observed about the Moon. Does it change?
Choose a child to hold the fruit representing the Moon. The child's head will represent our Earth. Choose another child to stand with a large flashlight in the corner of the room (or use a lamp); the lamp will represent our Sun. Before turning on the “Sun,” ask the children to observe the fruit.
Does the fruit make its own light? (No)
Does our Moon make its own light? (No)
Turn the light on and direct it toward the fruit. Invite the children to observe the bright side of the fruit that is reflecting the light, just like our Moon does.
When we look at the Moon, if it does not make its own light, why does it look so bright — where does the Moon get its light? (Our Sun; in the same way that the Sun illuminates Earth, our Moon reflects the Sun's light, making it bright in our sky)
Ask the children why we do not always see a full Moon, illuminated by our Sun, from Earth.
Have the child holding the fruit position it at arm's length, pointing at the light. Invite the other children to stand behind the “Moon.”
What do they observe about the Moon? Is the part of the Moon they see from Earth illuminated? (N)
What part is illuminated? (The part facing the “Sun” that they cannot observe from “Earth”)
Invite the children to move around the Moon to observe the side that is illuminated.
Is the side of the Moon facing the Sun always illuminated? (Yes, just like the side of Earth facing our Sun always is illuminated)
What phase of the “Moon” are they observing from “Earth”? (The new Moon)
Ask the child holding the “Moon” to slowly turn 180 degrees, or a half-circle in the direction that our Moon orbits Earth, keeping the Moon at arm's length. Invite the other children to share their ideas of the Moon's direction of revolution. (Counterclockwise if viewed from above in the northern hemisphere; or to the left)
What happens to the illumination of the Moon's surface as viewed from the Earth, as the Moon's position changes? (It increases until the side facing Earth is fully illuminated)
Make sure that all the children observe the change in illumination; they will have to move so they are observing the Moon from the same direction as the child holding the Moon.
What phase of the Moon are they observing? (The full Moon)
Once the children are comfortable observing the changing illumination of the Moon, repeat the exercise so that each Moon phase is revealed. Start with the new Moon and have the child holding the fruit rotate in steps of 45 degrees, pausing at each phase to invite the children make observations about the illumination and to identify the phase.
The children may wonder about Earth's rotation and the movement of our Moon. Remind them that Earth is spinning once on its axis each day, while our Moon is orbiting Earth approximately once each month (and spinning on its axis at that rate, too!). To illustrate this, pause the activity periodically and have another child hold the Moon wherever it is in its cycle. Have the child representing Earth spin slowly counterclockwise. Invite the other children to make observations about Earth's day and night cycle relative to the illumination of the Moon.
Invite the children to continue their exploration, having them exchange roles. Ask them recount the patterns of changing illumination they observe. Use randomly selected cards of the Moon's shape to challenge them to explain the positions of our Sun, Earth, and Moon.
Explore eclipses using the same materials.
Ask the children what an eclipse is. Invite them to use their fruit Moon and light Sun to make an eclipse of the Moon happen.
Let the children experiment. When they think they have the answer, ask them to share.
Lunar eclipses occur when the Earth is between the Sun and the Moon and the Moon is in the shadow of the Earth. Is this what the children are demonstrating? A solar eclipse occurs when the Moon is between the Sun and Earth.
Ask the children what they observe about a lunar eclipse.
What has to happen? (The Moon, Earth, and Sun have to be in a line so that the shadow of the Earth “covers” the Moon)
During what phase of the Moon can lunar eclipses occur? (Only during the full Moon phase)
How can they explain that during the full Moon the Moon is fully illuminated, yet during an eclipse, with the same order of the Sun, Earth, and Moon, the Moon is in shadow?
Alternatively, do we have a lunar eclipse every month? (No) Why not?
Invite the children to demonstrate the lunar eclipse again. Ask them to demonstrate the full Moon.
What do they have to do to make the full Moon? (Raise or lower their arms so that the Moon is in the path of the Sun's light)
Remind the children that Earth goes around our Sun. Its orbit makes a plane. Likewise, ourMoon goes around Earth. It also traces a plane — the orbital plane. However, the Moon's orbital plane is tilted a little to Earth's plane (by about 5 degrees) and is a bit elongated, making an oval-shape — an ellipse.
Every month the Moon moves around its inclined plane. As the Moon orbits Earth, it only intersects Earth's orbital path at two points — or twice each month (think of two crossed Hula Hoops; there are two places they touch). These two times are the only times when Earth, the Moon, and the Sun are in the same plane.
In order for an eclipse to occur, the Earth, Moon, and Sun must be in the same plane, and the Moon must be in the position of a full Moon (lunar eclipse) or a new Moon (solar eclipse). Most of the time during the full Moon — when a lunar eclipse is possible, the Moon is a little above or a little below Earth's shadow — it misses the shadow and we see the full Moon. Occasionally, the Earth and Moon and Sun are aligned so that the Moon is in Earth's shadow, and then we see a lunar eclipse.
The Moon's plane of orbit stays oriented in nearly the same direction in space as it moves with Earth around the Sun once a year. With this orientation, the geometry is correct for the Sun, Earth, and Moon to be in the same plane at the same time the Moon is in full or new phase twice a year.
However, eclipses vary in timing from year to year. This is because the Moon's elliptical plane of orbit shifts or turns a little each year, moving the timing of eclipses.
Invite the children to move their Moons in an inclined orbit to demonstrate phases and the occasional lunar eclipse.
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