When the moon is aligned with and between the Earth and the sun, it's a New Moon phase.

Here's why:

* Alignment: The moon is directly between the Earth and the sun.

* Sunlit Side: The side of the moon facing the sun is completely illuminated, but since the moon is between us and the sun, we can't see it from Earth.

* Appearance: We see the moon as a dark, invisible disc in the sky.

Let me know if you'd like to know more about other moon phases!