Here's why:

* Constellations are patterns of stars: They are groupings of stars as seen from Earth, but these stars are not physically connected.

* Earth is a planet: It orbits the Sun and is not a star.

* Earth's position changes: As Earth orbits the Sun, our view of the constellations changes throughout the year.

So, while we can see constellations from Earth, Earth itself isn't a part of any constellation.