Moon phases
Fly around a real 3D Moon, then stand on Earth and look up. The phase is which part of the lit half faces you.
Waxing crescent. Lit on the right.
What students walk away with
- 1The Sun always lights half the Moon. The phase is how much of that lit half faces Earth.
- 2Phases repeat every 29.5 days because the Moon orbits Earth, in a fixed order.
- 3Each phase keeps its own schedule: a full Moon rises at sunset, a first quarter Moon at noon.
Standards
- MS-ESS1-1 Patterns of the Earth, Sun, and Moon
Sim. Grades 6 to 12. Question sets for middle school, high school, and upper high school.
How the model works
Nothing is to scale. The Moon is really about 30 Earth diameters away and a quarter of Earth's width; here it is drawn at half Earth's width, about 4 Earth radii out, so the whole orbit fits and the lit half is easy to see.
The orbit is drawn flat in Earth's orbital plane and Earth's shadow is not drawn, so eclipses are not modeled. The real orbit is tilted about 5 degrees, which is why most new and full moons pass above or below the Sun's line and no eclipse happens. Earth's tilt is left out too.
Sky times are for a mid-latitude northern observer facing south, with sunrise at 6 AM and sunset at 6 PM as at an equinox. Moonrise comes about 50 minutes later each day on average; the real delay ranges from roughly 20 to 70 minutes with the season and latitude.
A cycle is the 29.5-day synodic month, new moon to new moon. The Moon circles Earth once against the stars in 27.3 days; the extra two days are because Earth has moved along its own orbit, so the Moon has farther to go to line up with the Sun again.
Run it with a class
Pick the questions, get a class code, and watch answers arrive live. Students need only a first name.
Set up an assignment