Is it possible to distinguish a photo of a sunrise from one of a sunset?

Human activities also drive a divergence between them. "At sunset the sky is full of pollutants and wind-borne particles," the authors write. "During the night, winds die down, smog-producing urban activity eases and the atmosphere cleanses itself. The dawn is clearer than any other time of day."

It's a matter of opinion whether pollution or a lack of it makes for prettier twilights. At dawn, clearer skies enable more brilliant reds and oranges to make their way through the atmosphere to your eyes, whereas thicker atmospheres at dusk tend to dull these colors, leading to more washed-out sunsets. On the other hand, more dust and smog (at sunset) can have the effect of scattering light across a greater region of the sky, creating a larger drape of colors, whereas sunrise colors tend to be more focused around the sun. Whichever you prefer, you can frequently tell a sunrise from a sunset by the fact that the latter appears more chaotic, and the former, tidier.