What is a New Moon? - Definition & Phases

What is a New Moon? - Definition & Phases
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  • 0:01 When the Moon Disappears
  • 0:44 New Moon & Phases of the Moon
  • 2:51 A Solar Eclipse
  • 3:25 Lesson Summary
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Lesson Transcript
Instructor: Mary Ellen Ellis
Once, or sometimes twice, a month, the moon disappears from our view. This is called a new moon, and it happens when the illuminated side of the moon faces away from us. You'll learn all about it in this lesson.

When the Moon Disappears

Whenever you look up into the sky, day or night, and see the moon, you are seeing it in one of its many phases. The way we see it from Earth changes every day and depends on the alignment of three important celestial bodies: the sun, the earth, and the moon itself.

If you have ever noticed that the moon is absent, it may be that you are viewing a new moon. The new moon is the phase of the moon that is invisible from Earth. The moon is situated between the earth and the sun so that the side that is illuminated by the sun's rays faces away from us. The moon is still there; we just can't see it.

The New Moon and the Phases of the Moon

Sometimes you can't see the moon because it is the new moon, but there are other explanations, too. The moon may be hidden behind a building, or it may not have risen yet. The time at which the moon rises and sets varies much more than sunrise and sunset. Sometimes the moon comes out in the day and is difficult to see, especially if it is cloudy. About once a month, though, the moon is invisible to you because it is new.

The phases of the moon are the different appearances of the illuminated moon from our vantage point on Earth. The moon itself doesn't change, but the part of it that is reflecting sunlight is visible to us to different degrees depending on how the earth, moon, and sun are positioned relative to each other. For instance, when the earth is in between the moon and the sun we can see one side of the moon, fully illuminated by the sun. It looks perfectly round, and we call this the full moon.

When the moon is situated between the earth and the sun, the illuminated side of the moon faces away from the earth, and we can't see it. We call this the new moon. A day or two after the new moon, you can see a skinny crescent-shaped moon. It gets bigger and bigger until it reaches the full moon, then it wanes again, becomes a crescent, and finally goes back to being a new moon. This is called the lunar cycle, and it takes approximately 29 days from one new moon to another.

The lunar cycle mostly coincides with a calendar month, but not completely. This means you will typically see (or not see) a new moon once a month, but sometimes there will be two in a month. The second new moon in a month is called a black moon. Like a blue moon (the second full moon in a month), a black moon occurs every two and a half years or so. The black moon doesn't get as much attention as a blue moon, which makes sense since you can't actually see a black moon.

In most cultures, including modern western culture, the new moon is considered the start of a lunar cycle. Each lunar cycle begins and ends with the new moon, and the full moon falls at the halfway point of the cycle.

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