 |
| The Trifid Nebula is a fine example of an object which combines emission and reflection nebulosity. The striking red emission nebula surrounds a small group of very hot stars. Energetic radiation from these stars causes part of the enveloping but otherwise invisible hydrogen cloud to fluoresce and emit its characteristic monochromatic red light. Beyond the limits of the emission nebula sufficient starlight escapes at longer wavelengths for it to be scattered by the dust grains associated with the gas. The scattering produces a faint blue reflection nebula around the irregular sphere of red emission. To the north, a star which is too cool to create anemission nebula is embedded in its own hazy blue reflection. |