What is a nebula?

• A. A bright star at the center of a galaxy
• B. A large cloud of dust and gas where stars begin
• C. A planet's atmosphere
• D. A type of galaxy

Answer: (B)

A nebula is a vast cloud of dust and gas in space where stars are born. These clouds are the raw material for star formation; gravity pulls material inward and, in dense pockets, protostars can ignite to form new stars. Nebulae can glow if hot young stars ionize the gas (emission nebulae), can reflect starlight (reflection nebulae), or can appear dark by blocking background light (dark nebulae). This helps distinguish it from a bright star at the center of a galaxy, which is a single stellar object; from a planet’s atmosphere, which is just the gaseous envelope around a planet; and from a type of galaxy, which is a huge system of many stars, gas, and dark matter. A familiar example is the Orion Nebula, a nearby star-forming region.