Astronomy Picture of the Day . ... It is visible as the dark indentation to the red emission nebula in the center of the above photograph. The horse-head feature is dark because it is really an opaque dust cloud that lies in front of the bright red emission nebula. ... Just to the lower left of the Horsehead nebula featured picture is a blueish reflection nebulae that preferentially reflects the blue light from nearby stars . ... Publications with keywords: Horsehead Nebula . ...