As the Moon orbits the Earth, the visible part of the Moon undergoes significant changes in illumination, leading to different lunar phases. Here’s a description of the changes you would observe:
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New Moon: When the Moon is positioned between the Earth and the Sun, the side of the Moon facing Earth is not illuminated, making it nearly invisible.
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Waxing Crescent: As the Moon moves out of the new moon position, a small sliver of the Moon becomes illuminated. The illuminated portion is less than half and is shaped like a crescent.
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First Quarter: When the Moon reaches a right angle with respect to the Earth and Sun, half of the Moon's face is illuminated. This is known as the first quarter phase.
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Waxing Gibbous: Continuing on its orbit, more than half of the Moon becomes illuminated, but it is not yet full. This phase is referred to as waxing gibbous.
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Full Moon: When the Moon is on the opposite side of the Earth from the Sun, the entire face of the Moon is illuminated, making it fully visible.
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Waning Gibbous: After the full moon, the illumination starts to decrease. More than half remains lit, but the light is now waning.
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Last Quarter: Similar to the first quarter, half of the Moon is illuminated, but now the other half compared to the first quarter is lit.
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Waning Crescent: As the Moon approaches the next new moon, only a small crescent is illuminated again, but this time it is on the opposite side than during the waxing crescent.
These changes in illumination are due to the relative positions of the Earth, Moon, and Sun. As the Moon orbits, the angle at which sunlight hits the Moon and the angle we observe it from Earth change, leading to the lunar phases.