A nebula is a vast cloud of gas and dust in space, often serving as a nursery for new stars. These clouds can be composed of hydrogen, helium, and other ionized gases. Nebulae can be observed in various forms, including emission nebulae, reflection nebulae, and planetary nebulae, each with distinct characteristics. Some nebulae are remnants of dead stars, while others are regions where new stars are forming. Famous examples include the Orion Nebula and the Crab Nebula. Studying nebulae helps astronomers understand the life cycle of stars and the composition of the universe.