Here's why:
* Earth's Tilt: The Earth is tilted on its axis, and this tilt causes the Sun to appear to move along a specific path in the sky throughout the year.
* Planetary Orbits: The planets in our solar system also orbit the Sun in a plane that is very close to the plane of Earth's orbit. This means they appear to move along a similar path in the sky.
* The Ecliptic: The apparent path of the Sun, Moon, and planets across the sky is called the ecliptic. It's essentially a projection of Earth's orbital plane onto the celestial sphere.
You can think of the ecliptic as a "highway" in the sky, along which the celestial bodies appear to travel.
