Sunset. Time-lapse photograph of the Sun setting over a coastline. The Sun is changing in brightness and colour as it sets. The Sun is also reflected in the water at each stage. 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 appear red. Photographed in Finland.