The four O stars of the Trapezium are identified and their luminosities determined. A reflection nebula shines by reflected starlight from nearby stars.
Reflection nebulae depend heavily on the presence of dust in the cloud.
Gas alone does not reflect light efficiently, and without the presence of dust particles, most nebulae would be essentially invisible. In all reflection nebulae it is the dust which is most reflective. Dust can also obscure our view of a nebula. A cold, dusty region in front of a reflection nebula will absorb the light from that nebula, and make that region appear dark. This effect is sometimes called a dark nebula .