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. However, it takes over 8 minutes for the light from the Sun to reach the Earth. During that time, the Sun's position in the sky changes by approximately 2 degrees. Near to the horizon, atmospheric refraction causes the ray path of light from the Sun to be distorted to such an extent that geometrically the Sun's disk is already about one diameter below the horizon when sunset is observed
Uploaded: Feb 2, 2016