What is a Nebula？ Astronomy and Space for Kids - FreeSchool

Space. It's vast, and full of secrets waiting to be discovered. Of all the incredible objects scientists have found out among the stars, some of the most spectacular are nebulae. Although most nebulae are completely invisible to the naked eye, modern telescopes are able to give us close-up views of some of the most beautiful objects in the galaxy. A nebula, named for the Greek word for cloud, is, in fact, an interstellar cloud of dust and gas. Like the clouds in the sky, nebulae come in interesting shapes, like flowers, insects, animals, or people. This is how many of them get their names. There are four main types of nebulae. First, there are star-forming regions, also known as stellar nurseries. In these huge areas of hydrogen gas, gravity pulls the materials together into large clumps, which in turn attract more material. More and more gas squeezes together harder and harder, making it grow hotter and hotter. When it becomes hot enough, it will be a new star. Whatever is left over may become planets, circling them. An example of a star-forming region, and one of the most famous nebulae in the sky, is the Orion Nebula. The Orion Nebula is the most active area of star formation in our galaxy. Although it is visible to the unaided eye, it is only a vague glow. Through a telescope, the extent of its wonder becomes visible. The Orion Nebula is 15 light-years across, and is made mostly of hydrogen. When you look at this nebula, you are looking at stars being born. This nebula gets its glow from something called the trapezium, a cluster of four stars, each thousands of times brighter than our sun. Their energy has cleared a space in the gases around them. You can see that other stars are being born inside the nebula too. These ovals are blankets of dust surrounding newborn stars. The rings inside are probably new planetary systems being formed around these stars. Thirteen hundred light-years away, the Orion Nebula is only a little glow in Orion's sword. Second, there are planetary nebulae. This kind of nebula doesn't really have anything to do with planets. But when early astronomers saw them through their telescopes, they looked so round and bright, they thought they must be planets. Planetary nebulae are formed by the slow death of ordinary stars. This beautiful object is known as the Butterfly Nebula, and it is an example of a planetary nebula. Although it looks peaceful, and like a delicate butterfly from afar, it is actually made of raging clouds of gas, heated to more than 36,000 degrees Fahrenheit. For comparison, that is more than three times hotter than the surface of the sun. The gas is also in motion, moving at more than 600,000 miles an hour. At that speed, you could go from the earth to the moon in just 24 minutes. The third kind of nebulae are called supernova remnants. Sometimes, when a star dies it doesn't die slowly, it dies with a bang. A supernova is a huge explosion that spreads the material from the star across a huge expanse of space. The leftovers form a nebula, which may over time collect and form new stars. The Crab Nebula is an example of a supernova remnant. This nebula is especially exciting because we know when the star that created it exploded. Nearly 1,000 years ago, Chinese astronomers noticed a bright new star in the sky. It stayed there for almost two years and then slowly vanished. Modern astronomers studying the Crab Nebula realized that the bright, temporary star described in the ancient record was an excellent match for the supernova that would have created the Crab Nebula. Knowing when the star went nova allowed scientists to learn a great deal about the way that this type of nebula develops. The fourth kind of nebulae are dark nebulae. A dark nebula is a cloud of gas and dust that is only visible because of the bright nebulae and stars behind it. Like a shadow or a silhouette, they take their shape from the light we do not see. One of the most famous dark nebulae is the Horsehead Nebula. It is easy to see where this nebula got its name. The Horsehead Nebula is made of thick dust clouds, so dense that they block the light of the stars behind them. Just because the cloud is dark does not mean that it is cold. Looking at the nebula through an infrared camera that allows us to look at the heat it gives off, we can see that the Horsehead Nebula is very hot indeed. There are even bright spots visible, which show where new baby stars are forming. No matter what type they are, nebulae are among the most dazzling celestial objects to be found in the sky. They are a window into the life cycle of the universe. In the end, the same raw materials that form stars are left behind when stars die, to form in turn new stars, and the cycle begins again. I hope you enjoyed learning about nebulae today. Goodbye till next time!