Nebula, NEHB yuh luh, is a cloud of dust particles and gases in space. The term nebula comes from the Latin word for cloud. Early astronomers also used the term for distant galaxies outside the earth's galaxy, the Milky Way. Such galaxies, called extragalactic nebulae, looked like hazy patches of light among the stars. But modern telescopes showed that extragalactic nebulae are actually systems of stars similar to the Milky Way.