What Will the Moon Do Next?

By Laura W. Somers • Illustrated by Cathy Beylon

This trick will help you to find out.

As you look up at the moon, you can use a simple trick to find out if it’s waxing or waning. We say the moon is waxing when it’s on its way to becoming full. We say the moon is waning when it’s losing a sliver each night.

Here’s the trick. Look at the moon, and draw an imaginary line where the center would be if the moon were full. Start at the bottom, and draw the line up the middle and past the top of the moon. The line and the lit side of the moon will form either a lowercase b or d.

The b stands for “baby.” The baby moon is on its way to the full-moon phase. It will appear to grow each night until it is perfectly round.

The d stands for “dying.” The dying moon is headed toward the new-moon phase. It will seem to become smaller each night until it can no longer be seen in the sky.

As the moon travels around the earth, the moon appears to change shape. But, in fact, the sun is simply lighting up different parts of the moon. No matter what phase the moon is in, you can use this trick. Every time, you’ll find that you’re right about what the moon will do next.

The red lines show how to tell whether a b or d is formed.