Nebulae are cosmic clouds of dust and gas floating in space. The word nebula is Latin and means cloud. Originally, the word nebula referred to any extended astronomical object, excluding comets, planets or satellites. But over time, the word nebula was reduced to designating an interstellar cloud of dust and gas. Calling it that doesn't do a nebula justice. Most nebulae generally consist of hydrogen and helium, dust and plasma. Nebulae are the building blocks of our universe; they contain everything stars need to form. Scientists classify nebulae into one of two broad categories: light and dark. From there, they narrow it down further to planetary nebulae, emission nebulae, reflection nebulae, dark nebulae, and supernova remnants. Bright nebulae are close enough to the stars to shine, and dark nebulae are too far from the stars to do so. Dark nebulae are only visible if a star cluster or other bright object provides a backdrop. Sometimes they are part of a bright nebula. A good example of this phenomenon would be the Trifid Nebula. It is a bright nebula divided into three sections by dark "alleys" running through it. Moving down the smaller categories, planetary nebulae form when a star cannot support itself through fusion reactions at its center. Gravity forces the sun's outer layers to focus on its core, causing the interior to heat and condense. Heat from the center blows outward in a stellar wind over a few thousand years. When the star ends, only the core remains. The core then heats the distant gases and they glow because of this. Although the planetary nebula is called planetary nebula, the planets have nothing to do with them. This is a very common nebula in our galaxy, as there is a middle of paper......began to classify and catalog objects in space that were not stars. Instead of using names, he gave them a number. For example, the Ring Nebula was and is classified as Messier Fifty-Seven or M57. The very first object that Mr. Messier classified was the Crab Nebula in Taurus, which Mr. Messier designated Messier one (M1). There are now one hundred and nine Messier objects recognized as M102 and have been accepted as re-observed M101. Then, in the 19th century, amateur astronomers began naming all objects Messier. Astronomers named most nebulae after the shape they resembled, which is how the Dumbbell and Owl Nebulae got their names. Some nebulae are named after the constellation they are part of, such as the Orion Nebula in the constellation Orion. As scientists and astronomers discover, classify and catalog nebulae, they are quite pretty. Nicknamed