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Glossary > O - Pg. 235

gloSSary 235 molecules like molecular hydrogen (H 2 ) to form. They are the birth sites of stars. Giant molecular clouds span hundreds of light-years and spawn thousands of stars, while small clouds, called Bok globules, may form just a few stars. molecule: A stable grouping of two or more atoms. nebula: A cloud of gas and dust in space. Some nebulae, like the Orion Nebula, are birth sites of stars and shine from the reflected light of newborn stars; others, like the Crab Nebula, are made of material ejected by dying stars. neutron: A subatomic particle with no electric charge and a mass slightly larger than that of a proton, usually found in atomic nuclei. neutron star: Dense, compact remnant of a massive star that exploded as a supernova. It is made almost entirely of neutrons.