MS-ESS1-1: Modeling Moon Phases, Eclipses and Seasons
Also called NGSS MS-ESS1-1 · Topic: Space Systems · Earth and Space Science
The Official Wording
Develop and use a model of the Earth-sun-moon system to describe the cyclic patterns of lunar phases, eclipses of the sun and moon, and seasons.
Clarification statement: Examples of models can be physical, graphical, or conceptual.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What MS-ESS1-1 Means in Plain English
Middle schoolers build and use a model of the sun, Earth and moon to explain three repeating patterns: the moon's monthly phases, solar and lunar eclipses, and the yearly seasons. The model can be a lamp and ball, a diagram or a computer simulation.
Students explain the patterns with positions, light and Earth's tilt, not with orbit math or exact eclipse dates. It builds on elementary sky patterns (1-ESS1-1, 5-ESS1-2) and leads to gravity's role in orbits (MS-ESS1-2).
MS-ESS1-1 I Can Statements
- I can use a model to show why the moon has phases.
- I can explain what lines up during a solar and a lunar eclipse.
- I can explain how Earth's tilt causes the seasons.
MS-ESS1-1 Worked Example
A classic phase model that a class can run in a darkened room with one lamp.
Why does the lit part of the moon change shape over a month?
Set It Up: A bare-bulb lamp as the sun, a foam ball stuck on a pencil as the moon, and each student's head as Earth, in a darkened room.
- Face the lamp and hold the ball at arm's length toward it.Lit side faces away: new moon
- Turn a quarter circle to the left, keeping the ball in front of you.Right half lit: first quarter
- Keep turning until your back faces the lamp, ball just above your head's shadow.Whole face lit: full moon
- Turn on to the three-quarter point.Left half lit: third quarter
- Return to the full moon spot and lower the ball into your head's shadow.Ball goes dark: lunar eclipse
The ball is always half lit by the lamp, and how much of that lit half we see depends on where the ball is in its orbit.
Why it works: The sun always lights half the moon, and as the moon orbits Earth over about a month, our view of the sunlit half changes.
Common Mistakes with MS-ESS1-1
Blaming phases on Earth's shadow
“The moon gets dark because Earth's shadow covers part of it.”
Try this: Earth's shadow causes only lunar eclipses. Phases come from seeing different amounts of the moon's sunlit half as it orbits Earth.
Explaining seasons by distance
“Summer happens when Earth is closest to the sun.”
Try this: Earth is actually closest to the sun in early January. Seasons come from the tilt, which changes how directly sunlight strikes each hemisphere.
Expecting an eclipse every month
“Every new moon should cause a solar eclipse.”
Try this: The moon's orbit is tilted about 5 degrees, so the sun, Earth and moon line up exactly only a few times a year.
Where MS-ESS1-1 Fits
Practice MS-ESS1-1
Quick Check
- During a full moon, where is the moon compared with Earth and the sun?
- What lines up during a solar eclipse?
- Why is it summer in the Northern Hemisphere in July?