Materials & Prep
- One lamp or bright flashlight for each group, with batteries if needed.
- One white foam ball or ping-pong ball on a pencil or craft stick for each student or pair.
- Board space for four phase sketches and the words new, crescent, quarter, gibbous, and full.
- Copy a phase investigation chart with columns for Moon position, observation, phase name, and evidence.
- Safety reminder: Confirm local procedures for using lamps or flashlights. Students should not stare directly into a bright light.
Opening prediction and phenomenon
DisplayDraw or show a simple sequence of a crescent, half-lit Moon, gibbous Moon, and full Moon. Ask, “If Earth’s shadow makes the Moon look different, why can we see several different shapes during a month without an eclipse?”
Have students commit: Students silently choose A, “Earth’s shadow changes the shape,” or B, “We see different amounts of the Moon’s sunlit half.” They may show one or two fingers, point, or write A or B. Tell them to keep this prediction so they can revise it later.
ConnectAsk students to recall what they already know about the Sun making light and the Moon reflecting sunlight. Do not correct the prediction yet. Say, “Today we will use a light-and-ball model to find out which explanation fits what we observe.”
Model the Sun, Earth, and Moon
ModelTurn off some classroom lights if useful. Place the lamp in the center. Explain the model clearly: the lamp represents the Sun, your head represents an observer on Earth, and the white ball represents the Moon. The bright half of the ball is the half facing the lamp.
Think aloudHold the ball between your head and the lamp. Say, “The lamp is lighting the side facing away from me, so I see almost none of the lit half. This position models a new Moon.” Move the ball slowly around your head while keeping it the same distance from your head. At the side, say, “Now I see half of the lit half, so this is a quarter phase.” Move it opposite the lamp and say, “Now the side facing me is fully lit. This is a full Moon.”
ConfrontAsk, “Did a dark object move across the ball and cover it?” Students should notice that the ball itself did not become darker because of Earth’s shadow. Explain, “Earth’s shadow can cover the Moon during a lunar eclipse, but a lunar eclipse is a special event when the Sun, Earth, and Moon line up. The ordinary phases happen because the Moon moves around Earth and we see different amounts of its sunlit half.”
Check for understandingHold the ball at a side position and ask, “What should I call this phase, and what part of the Moon is causing the bright shape?” Listen for “quarter phase” and “the visible part of the sunlit half.” If students say “Earth’s shadow,” return the ball to the model and ask them to point to the lamp, the observer, and the lit half.
Guided phase investigation
ExplainIn each group, the lamp stays in one place, the observer stays in the middle, and only the Moon’s position changes. One student is the observer, one holds the ball, and one records. Rotate jobs after four positions. The ball represents the Moon throughout the investigation, and the lamp represents the Sun throughout.
Display
Moon position Expected observation Phase Between lamp and observer Almost none of the lit half is visible New One-eighth around the observer A thin lit portion is visible Waxing crescent One-quarter around the observer Half of the visible side is lit First quarter Three-eighths around the observer More than half is lit Waxing gibbous Opposite the lamp The visible side is fully lit Full Five-eighths around the observer More than half is lit, but shrinking Waning gibbous Three-quarters around the observer Half of the visible side is lit Last quarter Seven-eighths around the observer A thin lit portion is visible Waning crescent
Have studentsMove the ball to each position, observe the ball from the same place, and record what they see before consulting the expected phase names. They should draw the visible bright shape in the observation column and then label the phase.
ScaffoldGive students the sentence frames, “I observe of the ball lit,” and “This is because the Moon is around Earth.” Point to the lamp and ball while students use the words lit half, visible half, waxing, and waning. Remind them that “quarter” names the Moon’s place in its orbit, not that only one-fourth of the visible Moon is lit.
Look forStudents should find that the phases occur in a repeating order: new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent, then new again. Ask groups to mark where the visible lit part grows and where it shrinks.
Substantial evidence and explanation
DiscussBring the class together to compare the new Moon, first quarter, full Moon, and last quarter observations. Ask, “What stayed the same in every position?” Expected response: the lamp lit one half of the ball. Ask, “What changed?” Expected response: the Moon’s position around the observer changed, so the observer saw a different amount of the lit half.
Worked exampleComplete one claim-evidence-reasoning response aloud. Claim: “The Moon’s phases are not caused by Earth’s shadow.” Evidence: “In our model, the lamp lit the same half of the ball at every position, and the ball showed different shapes as it moved around the observer.” Reasoning: “Because the visible shape changed when the Moon’s position changed, we saw different portions of the sunlit half. No Earth shadow was needed.”
StudentsUse their chart to write their own three-part response to the question, “What causes the Moon’s phases, and what pattern do they follow?” They must include one observation from the model and the phase sequence from new to full and back toward new.
ExtensionStudents who are ready should explain why a lunar eclipse is different from an ordinary phase. They should state that an eclipse requires the Sun, Earth, and Moon to line up so Earth’s shadow falls on the Moon, while ordinary phases result from viewing different portions of the sunlit half.
Closing check
Exit ticket: Students answer independently
- Put these phases in order beginning with new Moon: full, waxing crescent, waning crescent, first quarter.
- Explain in one or two sentences why a crescent Moon is not usually Earth’s shadow.
- Name what changes and what stays the same as the Moon moves through its phases.
Collect the tickets. A complete response identifies the repeating pattern, states that the Moon’s position changes what portion of its sunlit half is visible, and distinguishes ordinary phases from an Earth-shadow lunar eclipse.