Sunset over sea. The sun (with a distorted solar disc) sets over the ocean. The sky is clear. The distortions are caused by atmospheric turbulence and by air masses having different temperatures, densities and refractivities. As the sun sets, the solar radiation passes through an increasing mass of air which causes the sun to dim. The reddening is caused by particulate matter such as aerosols and dust suspended in the atmosphere. This particulate matter scatters blue light more strongly than red light, making the sun and surrounding sky appear red. Photographed over the Indian Ocean.