The word "nebula" is derived from the Latin word for "clouds". Indeed, a nebula is a cosmic cloud of gas and dust floating in space. More than one nebula are called nebulae. Nebulae are the basic building blocks of the universe. They contain the elements from which stars and solar systems are built. They are also among the most beautiful objects in the universe, glowing with rich colors and swirls of light. Stars inside these clouds of gas cause them to glow with beautiful reds, blues, and greens.