Why is the line dividing the light and dark sides of the half moon not perpendicular to the position of the sun when both can be seen in the sky during the daytime?

Answer 1

You can't see more than 50% of the moon's surface at any one time, and the

sun can't illuminate more than 50% of the moon's surface at any one time.

When the half you see is the same as the illuminated half, that's a Full Moon.

Answer 2

A 'half moon' is when the earth's position relative to the moon allows us to see half of the moon's face during its daytime, and the remaining half during its night time. Night time on the moon is the moon's own shadow on its unlit half. Night on earth is exactly the same thing.

However since the sun is the source of the light, nothing can cast a shadow over it in the same way. The only way to block it, is for a celestial body to move in front of it - the only one that is able to do that to a noticeable extent is the moon blocking our view of it during a solar eclipse.

Answer 3

The orbit of the moon is tidally locked to the Earth - it always keeps the same face to the earth so it pretty much makes one rotation for every orbit of the Earth (not EXACTLY one orbit since the earth is also orbiting the sun - but very close to one orbit). As it orbits, the half that is illuminated shifts but we still see just the same face so we never see portions of the back side illuminated.

Answer 4

Because the other half of the Moon is on the other side of the Moon, which we can't see.

Answer 5

It is. It may not LOOK that way, because we're seeing the round Moon from an angle. It's an optical illusion.