Sunset, also called sundown in some American English dialects, is the instant when the trailing edge of the sun's disk disappears below the horizon in the west. It should not be confused with dusk, which is the point at which darkness falls, some time after the beginning of twilight when the sun itself sets.

The Sunset is often more brightly colored than the sunrise,[citation needed] with the shades of red and orange being more vibrant. The atmosphere responds in a number of ways to exposure to the sun. In particular, there tends to be more dust in the lower atmosphere at the end of the day than at the beginning. During the day, the sun heats the surface of the Earth, lowering the relative humidity and increasing wind speed and turbulence, which serves to lift dust into the air. However, differences between sunrise and Sunset may in some cases depend more on the particular geographical features of the location from which they are viewed. For example, on a west-facing coastline, Sunset occurs over water while sunrise occurs over land.