My Full Moon is Square — Elinor J. Pinczes

The moon changes phases, of this, we're aware; but who ever heard of a full moon that's square?
It appears at the pond on the darkest of nights, when the bright little fireflies turn on their lights.

It's hard to read after dark, and a frog at the local pond is having just that problem. Realizing the frog's dilemma, a number of bright fireflies offer to help by illuminating the sky above him with both derring-do and a knack for mathematical precision. Through a series of square formations, the flies tirelessly search for the right equation to light the pond on a moonless night. Children will learn with ease from this creative tale about the power of co-operation and simple math.