why do we have a new moon

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. A solar eclipse occurs when the moon passes between the earth and the sun, blocking the sun from our view here on Earth.


This can only happen during a new moon, when the moon is between the earth and the sun. Why don't we get an eclipse once a month then? The reason is that the plane of the moon's revolution around the earth doesn't always line up with the earth and the sun. Most of the time when we have a new moon, the moon is a little above or below a straight line between the earth and the sun. Only when the new moon falls on this line do we get an eclipse. The phases of the moon are the different ways that we see the moon in the sky as it revolves around the earth and is illuminated by the sun. The new moon is the phase that is invisible to us here on Earth because the moon is between the earth and the sun, and its illuminated side is facing away from us. The new moon marks the beginning of the lunar cycle, the movement of the moon through its different phases. When there are two new moons in a calendar month, the second one is called a black moon.


A solar eclipse occurs when the moon moves in front of the sun, blocking it from our view on Earth. This can only happen during a new moon. Phases of the Moon New Moon Lunar Cycle Black Moon Solar Eclipse Eclipses only occur if the Moon is located within 0. 5 degrees of the plane of the ecliptic, on a line that passes through the center of the Sun and the Earth. The Moon travels along an orbit that is inclined by 5 degrees to the ecliptic plane, so there are only two opportunities each month when it passes through the plane of the ecliptic. These points are called the ascending and descending nodes. Eclipses of the Sun only occur if new moon occurs when the Moon is near of one of these nodes. A similar argument explains why lunar eclipses do not occur every full moon at the node opposite the Sun from the Earth.

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