A nebula is an interstellar cloud composed primarily of dust, gas, and plasma. These celestial structures represent some of the most fundamental building blocks of the cosmos, containing elements such as hydrogen and helium, along with heavier elements synthesized by previous stellar cycles. Nebulae are critical sites for stellar evolution, serving as stellar nurseries where the gravitational collapse of molecular clouds initiates the process of star and planetary system formation. Different types of nebulae are classified based on their appearance and composition, ranging from reflection nebulae, which shine by scattering the light of nearby stars, to emission nebulae, which glow due to the ionization of gases by intense ultraviolet radiation. The dispersal of nebular material also constitutes the endpoint for certain stellar types, forming visible remnants like planetary nebulae.