... Scorpius in Red and Blue . ... Credit Copyright: John Davis Explanation: Cosmic dust clouds dim the light of background stars. But they also reflect the light of stars nearby. Since bright stars tend to radiate strongly in the blue portion of the visible spectrum, and the interstellar dust scatters blue light more strongly than red, the dusty reflection nebulae tend to be blue. ... Of course, the contrasting red emission nebulae are also caused by the hot stars' energetic radiation. ...