In time for Halloween

The Witch Head Nebula, whose name goes without explanation. The nebula is associated with the star Rigel. in the constellation Orion. In the official catalog, the nebula is IC 2118. The blue glow comes from the reflected light of Rigel and from the fact that the dust grains in the nebula reflect blue light more efficiently than red light. This is similar to the timeless question of why our sky is blue...