Nebulae and star clusters.

Nebulae and star clusters

A nebula is of dust and gas inside a galaxy. Nebulae become visible if the gas glows, or if the cloud reflects starlight or obscures light when it is stimulated by radiation from hot young stars. Reflection nebula shine because their dust reflects light from in around nebula. Dark nebulae appear as silhouettes because they block out light from shining nebula or stars behind them. Tow types of nebula are associated with dying stars; planetary nebula and supernova remnants. Both consist of expanding of gas that were once the outer layers of star. A planetary nebula is a gas shell drifting away from a dying stellar core. A supernova remnant is a gas shell moving away from a stellar core at great speed following a violent explosion called supernova.  Stars are often found in groups known as clusters. Open clusters are loose groups of a few thousand young stars that were born from the same cloud and are drifting apart. Globular clusters are densely packed, roughly spherical groups of hundreds. Of thousand of older stars.

                         Emission nebula
This is image of beautiful emission nebula in our galaxy.




  

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