The Trifid Nebula (M20)

This multi-featured nebula in the constellation Sagittarius is about 5200 light years distant and 40 light years across. It is a region in which a cluster of new stars are forming. The red regions are caused by glowing hydrogen gas, excited by radiation from the hot young stars. The blue region is a reflection nebula, caused by dust preferentially reflecting passing light with shorter wavelengths (blue) than light with longer wavelengths (red). This is the same reason our daytime sky appears blue. The dark lanes are where cooler and somewhat closer dust clouds mask our vision of the colorful billows beyond. Through a telescope the brighter region seems divided into three by the dark lanes, hence the name Trifid Nebula.