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Star-forming region, the Eagle Nebula, M16 This is a picture of part of the Eagle Nebula. The word “nebula” refers to any cloud of interstellar gas and dust. In this picture, taken by the Hubble Space Telescope, young stars are forming in the “fingertips” that stick out of the larger columns of gas and dust. Planetary nebula, NGC 2392 (The Eskimo Nebula) The word “nebula” refers to any cloud of interstellar gas and dust. Through small telescopes, these objects looked like the planets Uranus and Neptune, and so early astronomers called them “planetary” nebulae. Astronomers now know that they have nothing to do with planets, but the name has stuck. Our own Sun will eventually, billions of years from now as it nears the end of its life, will sit at the center of a planetary nebula of glowing gas, perhaps like this one. This object is known as the Eskimo Nebula, because it resembles a face enclosed by a fur parka Supernova remnant, The Crab Nebula, M 1 Astronomers also see areas in which gigantic stars have literally blown themselves to pieces. The stellar explosion, called a supernova, which led to the formation of the Crab Nebula, shown in this picture, was witnessed by Chinese astronomers in 1054 A.D. One night they noticed that an extremely bright star had appeared in the sky where before there had seen nothing. It remained visible for over a year, before slowly fading from view. Centuries later, when astronomers look where the Chinese saw the “guest star,” they see this nebula of glowing gas and dust, the remains of a once massive star. Black hole candidate, Cygnus X-1 With their telescopes, astronomers have found evidence for black holes. Black holes are incredibly dense objects with such high gravity that not even light can escape from them, if it gets too close. This artist’s drawing shows one possible black hole, called Cygnus X-1. Gas from the large star at the right is falling onto a disk around the black hole at the left. As this disk material swirls around and falls into the black hole, it gives off X-rays, which is how astronomers were able to “see” the otherwise “black” hole. Interstellar Cloud, the Trifid Nebula, M20 When they look through their telescopes, astronomers also see enormous interstellar clouds of gas and dust. Part of this interstellar cloud, known as the Trifid Nebula, appears blue because it is reflecting light from nearby stars. The red part of the cloud is glowing hydrogen gas, lit up by ultraviolet radiation from a star embedded deep within it. The Pleiades star cluster, M45 Astronomers also see clusters of hundreds of stars, all born from the same giant interstellar cloud. This group is called the Pleiades (Plee-a-deez), and can be seen with the unaided eye in the constellation Taurus the Bull. Spiral Galaxy, M 81 Astronomers also see collections of billions of stars known as galaxies. This one, known as M 81, has two “arms” full of stars that spiral out from its center. Artist’s drawing of planet orbiting 51 Pegasi And in recent years, astronomers have begun to see evidence that planets orbit around stars other than the Sun. This artist’s drawing shows a giant planet orbiting the star 51 Pegasi. It was the first planet discovered outside of our solar system.