2026–27 · Backup lesson · Summer & ESY 2027
Read Moon Phases with a Light Model
Adult extension of: Moon Phases
Unscheduled alternative · available resource
Use a lamp and ball to model why the Moon’s illuminated portion appears to change across a lunar cycle. Build an observation plan that records date, time, and viewing conditions without confusing ordinary phases with an eclipse.
Curriculum skill focus: Pattern recognition, visual tracking, astronomy, sequencing
01 · Learning
Objectives
- Explain that the Sun illuminates roughly half of the Moon at a time.
- Relate changing viewing geometry to the visible illuminated portion.
- Distinguish a Moon phase from Earth’s shadow during a lunar eclipse.
02 · Preparation
Materials
Cool LED lamp with stable base; white ball on a safe stand or handle; Earth marker; phase cards; dated lunar photographs; observation sheet; clear indoor walking space.
03 · Practice
Adult project
- 1
Examine dated Moon photographs and name what changes in appearance. Predict whether the Moon changes its physical shape or the portion of its sunlit half we can see changes, using any preferred response method.
- 2
Set a cool lamp as the Sun, an observation position as Earth, and a ball as the Moon. Keep the observer clear of the light path and arrange the ball slightly above or below the Earth-shadow line so ordinary phases are not modeled as eclipses.
- 3
Move the ball slowly around the observer’s position, or have a partner move it while the observer stays seated. Pause at several positions and describe the illuminated part visible from that viewpoint.
- 4
Match those views with new, quarter, and full phase cards, adding crescent and gibbous where useful. Explain that quarter names refer to position in the cycle while about half the visible disk is illuminated.
- 5
Show separately how Earth’s shadow can fall on the ball only when the model is deliberately aligned. Label this as an eclipse demonstration and explain that the real Moon’s tilted orbit prevents a lunar eclipse every month.
- 6
Create an optional log with date, time, direction, cloud cover, and observed appearance. Use supplied dated photos when the Moon is unavailable, and compare several observations rather than promising a particular phase tonight without checking.
Evidence & interpretation
What the investigation shows
Moon phases reflect the changing portion of the sunlit lunar hemisphere visible from Earth over about 29.5 days. Ordinary phases are not caused by Earth’s shadow; that shadow is involved in a lunar eclipse.
Practical connection
Why this work matters
Moon observations offer a repeatable outdoor record-keeping activity and help interpret calendars and sky photographs.
Participation by choice
Individual access options
- Remain seated while a partner moves the ball, or use a tabletop Earth marker and fixed camera view.
- Use high-contrast phase cards, tactile half-lit models with descriptions, or enlarged dated photographs.
- Choose a well-lit photo-based sequence if dim lighting or movement is uncomfortable; pause, watch only, or decline outdoor observation.
Review & transfer
Reflect on the work
- What changed in the model even though the ball kept the same shape?
- How is a lunar eclipse different from an ordinary crescent Moon?