Here's why:
* Earth's Rotation: Our planet spins on its axis from west to east. This rotation makes it *appear* as if the celestial objects are moving across the sky from east to west.
* The Celestial Sphere: We imagine the stars are fixed on a giant sphere, called the celestial sphere, surrounding Earth. As Earth rotates, it's like we're looking at different parts of this sphere.
Important Note: The specific point on the eastern horizon where a constellation rises changes throughout the year due to:
* Earth's Orbit: As Earth orbits the sun, our view of the constellations changes.
* The Tilt of Earth's Axis: Earth's axis is tilted, which causes the constellations to appear at different locations in the sky throughout the year.
So, while all constellations rise in the east and set in the west, the exact point of their rising and setting changes with the seasons and the position of the observer on Earth.
