That Sunset or sundown is the daily disappearance of the Sun below the horizon as a result of Earth’s rotation.
The time of sunset is defined in astronomy as the moment the trailing edge of the Sun’s disk disappears below the horizon in the west. The ray path of light from the setting Sun is highly distorted near the horizon because of atmospheric refraction, making astronomical sunset occur when the Sun’s disk is already about one diameter below the horizon. Sunset is distinct from dusk, which is the moment at which darkness falls, which occurs when the Sun is approximately eighteen degrees below the horizon. The period between the astronomical sunset and dusk is called twilight.
Sunset creates unique atmospheric conditions such as the often intense orange and red colors of the Sun and the surrounding sky. (From Wikipedia).
These are a few captures of disappearances of the sun below the horizon, and the resulting unique atmospheric conditions, as viewed from Annisquam.