Sunset or sundown is the daily disappearance of the Sun below the western horizon, as a result of Earth’s rotation.
The time of sunset is defined in astronomy as the moment when the trailing edge of the Sun’s disk disappears below the horizon. The ray path of light from the setting Sun is highly distorted near the horizon because of atmospheric refraction, making the sunset appear to occur when the Sun’s disk is already about one diameter below the horizon. Sunset is distinct from dusk, which is the time at which the sky becomes completely dark, which occurs when the Sun is approximately eighteen degrees below the horizon. The period between sunset and dusk is called twilight.
Locations north of the Arctic Circle and south of the Antarctic Circle experience no sunset or sunrise at least one day of the year, when the polar day or the polar night persists continuously for 24 hours.
Sunset creates unique atmospheric conditions such as the often intense orange and red colors of the Sun and the surrounding sky.
For the terms “civil twilight” and “astronomical twilight”, see Twilight#Definitions
Sunset is the point at which the Sun is first completely below the horizon marking the start of twilight. It should not be confused with dusk, which occurs at the end of twilight.
The 16th-century astronomer Nicolaus Copernicus was the first to present to the world a detailed and eventually widely accepted mathematical model supporting the premise that the Earth is moving and the Sun actually stays still, despite the impression from our point of view of a moving Sun. Read more