Orion Nebula

The Orion Nebula contains one of the brightest star clusters in the night sky. With a magnitude of 4, this nebula is easily visible from the Northern Hemisphere during the winter months. It is surprising, therefore, that this region was not documented until 1610 by a French lawyer named Nicholas-Claude Fabri de Peiresc. On March 4, 1769, Charles Messier inducted the Orion Nebula, M42, into his list of stellar objects. Then, in 1771, Messier released his list of objects for its first publication in Memoires de l'Academie.1 The Orion Nebula is one of the closest stellar regions to the Earth. Using parallax measurements, it has been estimated that this nebula is only 1,500 light years away. In addition, the Orion Nebula is a relatively young star cluster, with an approximate age of less than one million years. It has even been speculated that some of the younger stars within the cluster are only 300,000 years old. The Orion Nebula is an emission nebula because of the O-type and B-type stars contained within it. These high-temperature stars emit ultraviolet (UV) light that ionizes the surrounding hydrogen atoms into protons (H+) and electrons (e-). When the protons and electrons recombine, the electrons enter a higher energy level (n=3). Then, when the electron drops from the n=3 level to the n=2 level, an Hphoton is emitted. 2 This photon has a wavelength of 6563 Å, and therefore corresponds to the red portion of the visible spectrum. It is these H photons which give the nebula the distinctive red color which we see. The extreme brightness of the O-type and B-type stars, coupled with the Earth's atmosphere, has always made high-resolution imaging of the star-forming region difficult. But recent advances in adaptive optics and the repair of the Hubble Space Telescope have allowed for incredible detail into the center of the dust cloud. 3 The technological advances have also helped reveal several faint stars within the

Bibliography: Bless, R.C. Discovering the Cosmos. University Science Books. Sausalito, California. 1996. University Press. 1995.