What is a nebula?

A nebula is a cloud of gas and dust in space. Some nebulae (more than one nebula) are regions where new stars are being formed, while others are the remains of dead or dying stars. Nebulae come in many different shapes and sizes. There are four main types of nebulae: planetary nebulae, reflection nebulae, emission nebulae, and absorption nebulae. The word nebula comes from the Latin word for cloud.