Sunset and Sunrise
 

Sunset is the daily disappearance of the sun below the western horizon as a result of the Earth's rotation.
 
The time of sunset is defined as the moment the trailing edge of the sun's disk disappears below the horizon. Last light or dusk is the moment at which darkness falls, when the sun is about eighteen degrees below the horizon. The period between the astronomical sunset and dusk is called twilight.
 
Sunrise is the instant at which the upper edge of the Sun appears above the horizon in the east. dawn is the point at which the sky begins to lighten, some time before the sun itself appears.