A specific phase exists when the sun lies not more than 6 degrees beneath the either horizon during sunrise or sunset. During this time, people can easily distinguish the horizon, and if the atmospheric conditions are favorable (which means no moonlight or any other additional sources of light), the brightest stars become visible. Despite the diminishing light, individuals can still engage in various regular outdoor activities without any interruption.
When the sun’s position changes between 6 and 12 degrees below the horizontal line during either the sun’s rise or fall, the horizon remains distinct. The silhouettes of objects may become apparent even without the need for man-made lighting. However, during this stage, engaging in ordinary outdoor tasks without supplementary sources of light becomes a challenge, if not impossible.
The next phase is characterized by the positioning of the sun at a range between 12 and 18 degrees below the horizon, once again during either sunrise or sunset. During this duration, the sun’s light does not play a significant part in brightening the sky. This is true before the said time in the morning, and after in the evening.
At the onset of morning astronomical twilight and at the culmination of the same during the evening, the illumination of the sky is exceptionally faint. In several scenarios, it may even be so negligible that it’s virtually undetectable.
Another concept of importance is that of ‘Civil Sunset’, and it is devised by subtracting the time of ‘Civil Sunrise’ from it. Essentially, it denotes the time the sun officially sets, marking the ending of daytime and the beginning of nighttime.
A similar term, ‘Actual Sunset’, is also used and is calculated by deducting the time of ‘Actual Sunrise’ from itself. This, however, corresponds to when the sun physically disappears below the horizon marking the end of daylight.
Furthermore, alterations in the length of daylight between one day and the next are often observed and recorded. These changes can be directly linked to the shifting positions of the sun over the course of time, which, in turn, affects the durations of daylight and darkness throughout the year.