Blue Marble

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.

Assign to a class
SunlightNew moonFirst quarterFull moonLast quarterDrag the Moon
SunEastSouthWest
Seen from above You Your sky
Day of the cycle4.4 of 29.5
From Earth
Waxing crescentLit on the right20% litRises 9:30 AM

Waxing crescent. Lit on the right.

What to notice

Turn on Show the halves and drag the Moon around. Compare the amber half with the blue half, then check the From Earth card.

Jump to a phase
For teachers

What students walk away with

  1. 1The Sun always lights half the Moon. The phase is how much of that lit half faces Earth.
  2. 2Phases repeat every 29.5 days because the Moon orbits Earth, in a fixed order.
  3. 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

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, so eclipses are not modeled, and Earth's tilt is left out. Sky times are for a mid-latitude northern observer facing south. A cycle is the 29.5-day synodic month, new moon to new moon.

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