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Grade 6 · Science · 30 minutes

Unit 3 · Patterns and Design · Lesson 1 of 2

Why the Moon’s Shape Seems to Change

Use a top-view paper model to distinguish illumination from Earth-based appearance.

Mr. S Teaches · Original starter mini-lesson · MS6-SCI-05

Learning objective

Explain two Moon phases using the Sun–Earth–Moon positions and the observer’s viewpoint.

Before you begin

  • Know that the Moon reflects sunlight.

Gather your materials

  • Paper or notebook
  • Pencil and the passage, model directions or data printed in this lesson

Language to know

phase
The shape of the illuminated portion visible from a viewpoint.
orbit
A path around another object.
viewpoint
The position from which an observation is made.

Understand the concept

Moon model text: Sunlight normally illuminates half of the Moon. As the Moon moves around Earth, observers see different fractions of that lit half. Draw sunlight arriving from the right. A Moon to Earth’s right is near the new-Moon position; to the left, near the full-Moon position. Quarter positions lie above or below Earth in the top view. Ordinary phases are not caused by Earth’s shadow. Eclipses require more precise alignment than this flat model shows.

Teach it step by step

  1. Read the model text and place Earth in the center with sunlight arrows arriving from the right.
  2. Draw four Moon positions; shade the half facing away from the Sun at each position.
  3. Place a small observer at Earth and determine how much of the lit half is visible at the right, left and top positions.
  4. Explain why the flat drawing could falsely suggest an eclipse every orbit; mark that the real orbit is tilted.

Make the thinking visible

Worked example or model response

At the left position, the Moon’s right-facing half is sunlit and faces Earth, so the observer sees approximately a full Moon. At the right position, the sunlit side faces mostly away from Earth, giving a new Moon. The Sun still lights about half the Moon at both positions.

Guided practice

Together identify a quarter position and connect the phrase “half illuminated” with a sketch of the fraction visible from Earth.

Independent practice

Write a short explanation correcting “Earth’s shadow makes the Moon look half full.” Include two position labels and one limitation of the paper model.

Quick assessment

When the Moon appears full, has the Sun begun illuminating its entire sphere?

Answer key & assessment criteria

Answers and teaching guidance

  1. Guided: At a quarter position, the observer sees approximately half the illuminated half; half the visible disk appears lit.
  2. Independent: Phases arise from changing viewpoints of a sunlit half; Earth’s shadow is relevant to a lunar eclipse. The paper model leaves out orbital tilt and realistic scale.
  3. Quick check: No. About half the sphere is illuminated; more of that half is visible from Earth.

Look for: Look for a claim that answers this lesson’s question, accurate use of the supplied evidence and an explanation of a limit or alternative. Ask the learner to point to the detail supporting each inference.

Make it work for your learner

More support

Use a pre-drawn four-position diagram and physically turn the paper so the Sun direction remains clear.

Extension challenge

Explain how a tilted orbit helps account for why eclipses are less frequent than Moon phases.

Selected contributions · Official sources

Standards connections

Selected NGSS band contribution; not complete performance expectation coverage.

Contributes to NGSS performance expectation

MS-ESS1-1

NGSS · Grades 6–8 band

Use an Earth–Moon–Sun model to explain recurring patterns.

Read the official performance expectation ↗

This model addresses Moon phases only. Solar and lunar eclipses and seasons, also within the broader performance expectation, require additional modeling.

Source and mapping checked 2026-11-04. This mini-lesson contributes selected skills; it does not claim full attainment.

Supporting Common Core literacy connection

RST.6-8.7

Common Core · Grades 6–8

Connect scientific prose with a diagram, model or table.

Read the official standard ↗

The provided scientific passage/model is explicitly analyzed in the activity. This selected literacy practice does not establish subject-content alignment or complete coverage of the standard.

Source and mapping checked 2026-11-04. This mini-lesson contributes selected skills; it does not claim full attainment.