Here's why:

* Earth's Tilt: Due to Earth's tilt, different parts of the sky are visible at different times of the year.

* Pegasus's Position: Pegasus is located in the northern celestial hemisphere, and as the Earth orbits the Sun, our view of the northern hemisphere changes. In the autumn, the Earth's position allows us to see Pegasus most prominently.

You can find Pegasus in the evening sky, looking towards the east as night falls. It forms a distinctive square shape, which helps make it easy to spot.