Benchmark 4B
The Physical Setting: The Earth
Grades 6-8, page 69

The moon's orbit around the earth once in about 28 days changes what part of the moon is lighted by the sun and how much of that part can be seen from the earth--the phases of the moon.
 

NSES Content Standard D  Earth and Space Science: Earth in the Solar System  Grades 5-8, page 160  Most objects in the solar system are in regular and predictable motion. Those motions explain such phenomena as the day, the year, phases of the moon, and eclipses.