Towards the end of the day.

The end of the day can be extraordinarily beautiful. 

It might seem to be just a simple transition from light to dark, but astronomers recognise a number of distinct stages in the process.
It all starts with sunset, the daily disappearance of the Sun below the western horizon. The time of sunset is defined in astronomy as the moment when the trailing edge of the Sun's disk disappears below the horizon.

Sunset is followed by twilight, which is itself divided into three periods. Civil twilight lasts until the sun is 6 degrees below the horizon. Then there is a period of nautical twilight which ends when the the sun is 12 degrees below the horizon. Finally, astronomical twilight ends when the sun is 18 degrees below the horizon. Then it is night. It's as simple as that!