Nebulae are cosmic clouds of dust and gas that float in space. The word nebula is Latin and means cloud. Originally the word nebula referred to any large astronomical object, excluding comets, planets, or satellites. But over time the word nebula was reduced to meaning an interstellar cloud of dust and gas. Calling it that doesn't do the nebula justice. Most nebulae are commonly made up of hydrogen and helium gases, dust, and plasma. Nebulae are the building blocks of our universe; they contain all the things stars need to form. Scientists classify nebulae into one of two main categories; bright and dark. From there they further narrow it down to planetary nebulae, emission nebulae, reflection nebulae, dark nebulae, and supernova remnants. Bright nebulae are close enough to stars to shine, while dark nebulae are too far from stars to do so. Dark nebulae are visible only if a star cluster or other bright object is in the background. 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 into the smaller categories, planetary nebulae form when a star cannot sustain itself through fusion reactions at its center. Gravity pulls the sun's outer layers towards its core, causing the inner part to heat up and condense. The heat from the center blows away the outer parts in a stellar wind over a few thousand years. When the star ends, the only thing left is the core. The nucleus then heats distant gases and for this reason they glow. Although the planetary nebula is called a planetary nebula, planets have nothing to do with it. They are a very common nebula in our galaxy, as there is an e...... half of paper ......began to classify and catalog objects in space that were not stars. Instead of using names, he gave them numbers. For example, the Ring Nebula was, and is, classified as Messier fifty-seven or M57. The first object Messier classified was the Crab Nebula in Taurus, which Messier designated Messier one (M1). There are now one hundred and nine Messier objects recognized as M102 and it has been accepted that M101 has been reobserved. Then in the 19th century amateur astronomers began to name all of Messier's objects. Astronomers named most nebulae based on the shape they resembled, which is why the Dumbbell and Owl Nebulae got their names. Some nebulae are named after the constellation of which they are a part, such as the Orion Nebula in the Constellation of Orion. Even though scientists and astronomers discover, classify, and catalog nebulae, they're pretty cute. Nicknamed