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Teacher guide · Grades 3–5 · 30–35 minutes

One Moon, Three Evidence Checks

A device-free Claim–Evidence–Reasoning (CER) investigation. Suggested activity; not classroom-tested.

Learning goals
Distinguish a quarter of a lunar cycle from the illuminated portion visible from Earth; explain ordinary phases without Earth’s shadow.
Materials
Photocopied student sheet, pencils, optional matte white ball and teacher-controlled cool LED lamp. Paper-only use is valid.

Lesson sequence

  1. Predict — 5 min. Show three same-sized Moon disks and ask which represents First Quarter. Have each learner choose before discussing.
  2. Gather evidence — 12–15 min. Use the lamp-and-ball geometry below or paper drawings. Ask students to record two observations. Have them compare another Moon position as a control.
  3. Write CER — 10 min. Complete the claim, evidence, and reasoning spaces on the student sheet. Encourage evidence that can be described or sketched.
  4. Exit check — 5 min. Ask why “First Quarter” can appear half bright. Check for confusion about orbital stage versus visible illumination.

Where the lamp, ball and observer go

  1. Keep a cool LED lamp fixed, several times farther from the observer than the ball if possible. The teacher controls it and prevents direct glare.
  2. Observer (Earth) faces a matte white ball (Moon) held about an arm’s length away, at approximately eye height.
  3. From above, arrange the observer-to-ball direction roughly 90° from the observer-to-lamp direction. Keep the ball outside the observer’s own shadow. The observer looks at the ball, not the lamp.
  4. Sketch the roughly half-bright face. Then move the ball toward or away from the lamp direction, without moving the lamp, to compare phases.
LED lampObserverBall90°

Top-down schematic; distances and sizes not to scale. A nearby classroom lamp gives an approximate model.

Safety: Use a cool, low-glare lamp only. Never look directly into a bright lamp, use a hot bulb, or substitute the real Sun for the model.

Example student CER response (hypothetical, not pupil evidence)

Claim: First Quarter looks about half illuminated. Evidence: The side-facing ball looked bright on one half; moving it changed the bright portion I could see. Reasoning: The lamp continued to light half the ball, but my view changed. Earth’s shadow was not needed.

Differentiate: Provide sentence stems and labelled drawings for emerging writers. Challenge experienced students to compare Last Quarter and identify the model’s limits (size, distance, orbital tilt and observing orientation).

Scientific background: NASA Science, Moon Phases — https://science.nasa.gov/moon/moon-phases/ ; NASA LRO, Lunar Activities — https://science.nasa.gov/mission/lro/lunar-activities/ . Original printable drawings; no NASA images reused.

Student worksheet · Grades 3–5

Which Moon is First Quarter?

NameDate

1. Make a prediction. Circle the drawing you expect at First Quarter. All three circles show the same-sized Moon. Which part is bright?

A. One quarter bright
B. One half bright
C. Fully bright

Claim — What do you predict at First Quarter? Complete: “I think ____ because ____.”

2. Collect evidence. Have your teacher position the LED lamp (Sun), ball (Moon), and observer (Earth). Draw or describe two things you actually notice. You can also use the teacher’s paper diagram.

Evidence observation 1:

Evidence observation 2:

3. Explain your reasoning. How do the positions of the lamp, ball, and observer explain the bright part of the Moon? Why is it not Earth’s shadow?

Exit check: Why is this phase called “First Quarter” if you see about half of the Moon’s disk lit?

Model check: A classroom lamp and ball are not the real Moon system. Actual sizes, distances, the Moon’s tilted orbit, and the way it appears from different places are not to scale.