From the Latin 'nebula' (cloud), gas clouds and dust among the stars, nebulas are both active nurseries and graveyards of stars.
These splendors of the sky are illuminated by the stars they contain or by nearby stars located behind them.
These are the most beautiful astronomical images that can be achieved currently. Nebulas, we are admired in the telescope field of wonderful cities of stars and gas flooding the sky. More the telescope is powerful more images are beautiful and colorful.
Only long exposures reveal the entire palette of colors in particular the astonishing pink hydrogen. William Herschel discovered the dark nebulae, clouds of gas and dust without a star, too dense to leave, the light from stars behind.