Here's why:
* Filaments are cooler, denser clouds of gas that appear as dark, snake-like structures against the bright solar disk. They are essentially prominences seen from the side, appearing as if they are "resting" on the surface of the Sun.
* Prominences are large, bright, and often eruptive structures that extend from the Sun's surface into the corona. They can be much larger than filaments and are typically associated with more dramatic activity.
So, while both filaments and prominences are made of plasma and appear as clouds of gas, filaments are smaller, cooler, and less active than prominences.
