The moon is illuminated by sunlight, which reflects off its surface. As it orbits the Earth, different portions of the moon's surface are lit up by the sun, creating various phases. The main factors that determine how we see these phases are the relative positions of the Earth, moon, and sun.
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Sunlight Reflection: The moon itself does not produce any light; it merely reflects the sunlight that hits it. The amount of the moon’s surface that is illuminated and visible from Earth changes throughout its orbit.
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Phases of the Moon: As the moon travels around Earth, observers see different amounts of the illuminated portion. These phases range from new moon (when the moon is between the Earth and the sun and not visible) to full moon (when the Earth is between the moon and the sun, and the entire face of the moon is illuminated). The cycle of these phases takes about 29.5 days to complete.
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