Here's why:
* The Moon orbits the Earth: The Moon constantly orbits the Earth.
* Lunar Phases: As the Moon orbits, the angle between the Sun, Earth, and Moon changes. This changing angle is what causes the different phases of the Moon we see:
* New Moon: The Moon is between the Earth and Sun, so the sunlit side is facing away from us.
* Waxing Crescent: A small sliver of the moon becomes visible.
* First Quarter: Half of the moon appears illuminated.
* Waxing Gibbous: More than half of the moon appears illuminated.
* Full Moon: The moon is opposite the sun, so the entire sunlit side faces us.
* Waning Gibbous: The illuminated portion starts shrinking.
* Last Quarter: Again, half the moon is illuminated.
* Waning Crescent: The last sliver of the moon becomes visible.
* During a new moon: The Sun is illuminating the side of the moon facing away from Earth, so we cannot see it.
So, while the Sun is always shining, the Moon isn't always illuminated from our perspective.
