The shadow on the moon during daytime is cast by the Earth.

Here's why:

* Earth's position: During the day, the sun is on the opposite side of the Earth from the moon.

* Light and shadow: The sun's light shines on the Earth, and the Earth blocks some of that light from reaching the moon. This blockage creates a shadow on the moon.

* Lunar phases: The shape of the shadow (and the moon's illuminated portion) is what we observe as the different phases of the moon.

So, the shadow on the moon during the day isn't cast by the sun, but by the Earth itself, acting as a large obstacle in the path of sunlight!