<P> Most nebulae are of vast size , some are hundreds of light years in diameter . A nebula that is barely visible to the human eye from Earth would appear larger , but no brighter , from close by . The Orion Nebula , the brightest nebula in the sky that occupies a region twice the diameter of the full Moon , can be viewed with the naked eye but was missed by early astronomers . Although denser than the space surrounding them , most nebulae are far less dense than any vacuum created on Earth -- a nebular cloud the size of the Earth would have a total mass of only a few kilograms . Many nebulae are visible due to fluorescence caused by embedded hot stars , while others are so diffuse they can only be detected with long exposures and special filters . Some nebulae are variably illuminated by T Tauri variable stars . Nebulae are often star - forming regions , such as in the `` Pillars of Creation '' in the Eagle Nebula . In these regions the formations of gas , dust , and other materials `` clump '' together to form denser regions , which attract further matter , and eventually will become dense enough to form stars . The remaining material is then believed to form planets and other planetary system objects . </P>
<P> Most nebulae are of vast size , some are hundreds of light years in diameter . A nebula that is barely visible to the human eye from Earth would appear larger , but no brighter , from close by . The Orion Nebula , the brightest nebula in the sky that occupies a region twice the diameter of the full Moon , can be viewed with the naked eye but was missed by early astronomers . Although denser than the space surrounding them , most nebulae are far less dense than any vacuum created on Earth -- a nebular cloud the size of the Earth would have a total mass of only a few kilograms . Many nebulae are visible due to fluorescence caused by embedded hot stars , while others are so diffuse they can only be detected with long exposures and special filters . Some nebulae are variably illuminated by T Tauri variable stars . Nebulae are often star - forming regions , such as in the `` Pillars of Creation '' in the Eagle Nebula . In these regions the formations of gas , dust , and other materials `` clump '' together to form denser regions , which attract further matter , and eventually will become dense enough to form stars . The remaining material is then believed to form planets and other planetary system objects . </P>
gas and dust in interstellar nebulae can form -
gas and dust in interstellar nebulae can form -
stars
stars