The Phases of the Moon. Click on image for full size (15K GIF)

For example, if today the Moon were a waxing crescent, then we would only see a little piece of the half of the Moon that is reflecting sunlight. But tomorrow, that piece would be bigger. If today the Moon were a waning gibbous, then we would see a big piece of the half of the Moon that is reflecting sunlight. But tomorrow, that piece would be smaller.

There is an easy way to tell if a crescent Moon is growing or shrinking. If the crescent Moon looks like a "C" (C for collapsing!), it is shrinking.

The Phases of the Moon. Click on image for full size (15K GIF)

For example, if today the Moon were a waxing crescent, then tomorrow the crescent shape would continue to grow larger, approaching first quarter. After first quarter, the Moon would be a waxing gibbous, and continue growing until it reached full. The Moon would then begin to shrink, becoming first a waning gibbous and eventually reaching third quarter. Following third quarter it becomes a waning crescent, and continues to shrink until it becomes invisible at new Moon.

Just in case you can't remember all of this, there are a few handy ways to recognize whether the Moon is growing or shrinking. A crescent moon which looks like a "C" is shrinking (C for collapsing!). If it looks like a "D", then it is growing. This is true for a gibbous Moon as well, but it's a bit trickier to picture. If the edge of the Moon (the real edge of the Moon, not the edge of night on the moon) is curved like a "C", the gibbous Moon is shrinking. Another way to think of it is that the Moon always grows or shrinks from the right to the left.

The Phases of the Moon. Click on image for full size (15K GIF)

For example, if today the Moon were a waxing crescent, then tomorrow the crescent shape would continue to grow larger, approaching first quarter. After first quarter, the Moon would be a waxing gibbous, and continue growing until it reached full. The Moon would then begin to shrink, becoming first a waning gibbous and eventually reaching third quarter. Following third quarter it becomes a waning crescent, and continues to shrink until it becomes invisible at new Moon.

Just in case you can't remember all of this, there are a few handy ways to recognize whether the Moon is growing or shrinking. A crescent moon which looks like a "C" is shrinking (C for collapsing!). If it looks like a "D", then it is growing. This is true for a gibbous Moon as well, but it's a bit trickier to picture. If the edge of the Moon (the real edge of the Moon, not the edge of night on the Moon) is curved like a "C", the gibbous Moon is shrinking. Another way to think of it is that the Moon always grows or shrinks from the right to the left.