My almost-two-year-old loves the moon. (Hm, why do I feel like I’ve written that before?) One night around the time of the last full moon, he had trouble sleeping. So before putting him back to bed again, I took him outside to say good night to the moon. “Moom, moom, moom,” he said as he pointed, and while I smiled at the cuteness, I also hoped he wouldn’t want to say good night to the moon every night, because it wouldn’t be possible.
Full moons are easy, because at full moon, the moon rises at sunset and sets at sunrise. The moon gets its light from the sun, so in order to get a full moon, the moon has to be on the opposite side of the Earth from the sun. People experiencing night time on Earth then see a full disk of moon. Then, night after night, the moon appears smaller and smaller as it orbits the Earth, because we see less of the moon’s daytime side. The more the moon wanes, the later it rises, until it reaches new moon, a phase we can think of as “no moon,” because at this time the moon is between the Earth and the sun, and we see no part of the moon’s lit side. This also means that the moon appears in the sky near the sun, so the thin crescent moon is only seen at sunrise or sunset. Moonrise takes place about 50 minutes later each day than the day before. From one new moon to the next takes 29.5 days – about a “moonth.”
Here is a guide to help you keep track of the moon in its different phases:
- The New Moon always rises at sunrise and sets at sunset.
- A waxing crescent moon – sometimes called a young moon – is always seen in the west after sunset.
- The first quarter rises at noon, will be at its mid-point at sunset, and sets at midnight.
- A waxing gibbous moon* appears high in the east at sunset.
- The Full Moon always rises at sunset, will be at its mid-point at midnight, and sets at sunrise.
- A waning gibbous moon rises in the east between sunset and midnight.
- The last quarter rises at midnight, will be at its midpoint at sunrise, and sets at noon.
- A waning crescent moon – sometimes called an old moon – is seen in the east before dawn.
So, you will never see a crescent moon at midnight, nor will you see a last quarter moon at sunset, nor a full moon during the day.
* “Gibbous” may strike kids as a weird word. In the planetarium, I tell kids that they can remember “gibbous” by thinking, “Bigger than half, but not quite full. Gib’ us a little more light, and we’ll have a full moon!”