Sunset, also known as sundown, is the daily disappearance of the Sun
below the horizon due to Earth's rotation. As viewed from everywhere on
Earth (except the North and South poles), the equinox Sun sets due west
at the moment of both the Spring and Autumn equinox. As viewed from the
Northern Hemisphere, the sun sets to the northwest (or not at all) in
the Northern hemisphere's spring and summer, and to the southwest in the
autumn and winter; these seasons are reversed for the Southern
Hemisphere. The time of sunset is defined in astronomy as the moment
when the upper limb of the Sun disappears below the horizon. Near the
horizon, atmospheric refraction causes sunlight rays to be distorted to
such an extent that geometrically the solar disk is already about one
diameter below the horizon when a sunset is observed.
It is almost impossible to watch a sunset and not dream.