That's a great question! It's not entirely accurate to say the lighter halves of the Moon and Earth always face the Sun. Here's why:

The Moon:

* The Moon's phases are caused by its position relative to the Sun and Earth. The half of the Moon facing the Sun is illuminated, while the other half is in shadow. This creates the different phases we see from Earth.

* The Moon always presents the same face to Earth. This is due to a phenomenon called tidal locking, where the Moon's rotation period matches its orbital period around Earth. This doesn't mean the illuminated side stays the same. As the Moon orbits Earth, different portions of the illuminated side become visible from Earth, causing the phases we see.

The Earth:

* Earth's rotation is what causes day and night. The side of Earth facing the Sun experiences daylight, while the side facing away experiences night.

* Earth's orbit around the Sun causes the seasons. As Earth travels in its orbit, different parts of the Earth receive more direct sunlight, leading to warmer temperatures.

So, while the Sun illuminates one side of both the Moon and Earth, the "lighter" side isn't always the same. The illuminated side is constantly changing as these celestial bodies move.

Let me know if you'd like to learn more about lunar phases, tidal locking, or Earth's rotation and seasons!