Here's why:

* Constellations are patterns of stars. They are how humans have divided up the sky to make it easier to navigate and understand.

* The Sun is a star, but it's our star. It's the center of our solar system and everything orbits around it.

* The Earth orbits the Sun. This means that from our perspective on Earth, the Sun appears to move across the sky throughout the year, passing through different constellations.

So, while we might say the Sun is "in" a constellation at a particular moment, that's just because Earth's position makes it appear that way. The Sun itself doesn't belong to any constellation.