LiveEarth & Space ScienceMiddle School

Moon Phases: Light and Orbit

Half the Moon is always lit. The phase is which part of that half you can see.

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What students do

Explore how the Moon's phase depends only on its position in orbit, not on Earth's shadow. Drag it around to see how the lit fraction changes as it completes a full cycle in 29.5 days. Turn the orbit tilt on and off to see the difference: with a flat orbit an eclipse happens at every full and new moon, but the real 5-degree tilt makes eclipses rare. The model shows you why the pattern repeats predictably.

Standards alignment

MS-ESS1-1

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.

Practice: Developing and Using ModelsCrosscutting: Patterns