Sunset, also called sundown in some American English dialects, is the time at which the sun 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.
Mock mirage sunset in San Francisco
A composite image showing the terminator dividing night from day, running across Europe and Africa. Observers on the surface of the earth along this terminator will see a sunset.
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 during daylight hours. 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 geographical particulars of the location from which they are viewed. For example, on a west-facing coastline, sunset occurs over water while sunrise occurs over land.
The timing of sunset varies with the time of year and the latitude of the location from which it is viewed. The timing also varies in local time within a given time zone, determined by each location's precise longitude. Changes in timing of sunset are driven by the axial tilt of Earth, the spherical shape of the Earth, and the planet's movement in its annual orbit around the sun. Some apparent anomalies exist however. In the Northern Hemisphere, the earliest sunset does not fall on the winter solstice around December 21, but instead it occurs earlier in December. Likewise, the latest sunset does not fall on the summer solstice around June 21, but instead it happens later in June or in early July, depending on your latitude. The same phenomenon exists in the Southern Hemisphere except with the dates swapped. For one or two weeks surrounding both solstices, both sunrise and sunset get slightly later or earlier each day. Even on the equator, sunrise and sunset shift several minutes back and forth through the year, along with solar noon. This effect is plotted by an analemma.
Due to Earth's axial tilt, the direction of sunset in the northern hemisphere is always to the northwest from the March equinox to the September equinox, and to the southwest from the September equinox to the March equinox. Sunsets occur precisely due west on the March and September equinoxes, and the duration of day and night are precisely 12 hours on the Equinoxes for all viewers on Earth.
As sunrise and sunset are calculated from the leading and trailing edges of the sun, and not the centre, this slightly increases the duration of "day" relative to "night". Further, because the light from the sun is bent by the atmospheric refraction, the sun is still seen after it is below the horizon. This effect is a daily illusion along with sunrise. The sun also appears larger on the horizon, which is another optical illusion, similar to the moon illusion.
As a visual motif, sunset is often associated with summer, and (particularly when paired with a coconut palm) beach living and surfing culture. This may be due in the first instance to people spending more time outdoors in the evening during summer than during winter, and also because pictures of sunsets over the sea are often more spectacular than daytime beach scenes. Sunset is also a symbol of west, old age, ending, and closure.
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iftimus, Researcher at Beijing, favorited this 9 months ago
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