Nebulae
Scattered throughout the sky are vast interstellar clouds of dust and gas. These clouds are the stellar nurseries from which stars are born. Young hot stars ionize the gas within the clouds causing Fluorescence and the emission of light. This type of nebulae are called emission nebulae. Another type reflects the light from nearby stars and are termed reflection nebulae.
Two other types of Nebulae arise from stellar death. Planetary nebulae are visible as shells of gas surrounding a small white dwarf star. They are formed when low mass stars such as our sun reach the end of their lifespan and throw off their outer layers as the star itself collapses. In contrast, the death of massive stars results in a violent explosion termed a supernova. The resulting nebula is termed a supernova remnant.
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