We see the Moon at different phases due to its position relative to the Earth and the Sun as it orbits around the Earth. The phases of the Moon are a result of the changing angles of sunlight that illuminate the Moon as it travels in its elliptical orbit. Here’s a breakdown of the main phases and the reasons behind them:
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New Moon: The Moon is between the Earth and the Sun, so the side of the Moon that is lit by the Sun is facing away from the Earth. As a result, the Moon is not visible from Earth.
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Waxing Crescent: As the Moon moves in its orbit, a small sliver of the illuminated side becomes visible. This is called a waxing crescent.
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First Quarter: When the Moon has completed about a quarter of its orbit, we see half of the Moon's illuminated side. This is known as the first quarter phase.
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Waxing Gibbous: As the Moon continues to orbit, more than half of its illuminated side is visible, leading to the waxing gibbous phase.
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Full Moon: When the Earth is between the Moon and the Sun, the entire illuminated side of the Moon is visible from Earth, resulting in a full moon.
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Waning Gibbous: After the full moon, the amount of illumination starts to decrease, leading to the waning gibbous phase.
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Last Quarter: When the Moon is three-quarters of the way through its orbit, we once again see half of the Moon's illuminated side, but this time it’s the opposite half compared to the first quarter.
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Waning Crescent: As the Moon continues its orbit, only a small sliver of the illuminated side is visible again as it heads back toward the new moon phase.
This cycle of phases takes about 29.5 days, known as a lunar month, and is caused by the combined motions of the Earth and the Moon in relation to the Sun.