There exists a time frame when the sun stays a mere 6 degrees below the horizon during both dawn and dusk. This stipulates that the horizon must be distinctly visible, and it should be possible to sight the most brilliant stars given ideal atmospheric conditions, that is, in the absence of moonlight or any other sources of light. During this phase, routine exterior activities can be carried out without any impediment.
Progressing a little further, another time phase is defined when the sun position is between 6 and 12 degrees below the line of the horizon, regardless of whether it’s sunrise or sunset. During this phase, the border of the horizon is prominently visible and outlines of objects may become perceptible without the application of synthetic light. Unfortunately, common outdoor tasks cannot be enacted during this time span without auxiliary lighting.
Moreover, there’s a time span when the sun is between 12 and 18 degrees beneath the horizon at either sunrise or sunset. It is of interest to note that the sun doesn’t contribute to sky illumination prior to this specific time during the early hours, or post this time in the late evening hours.
At the commencement of the morning astronomical twilight and the concluding stages of the evening astronomical twilight, the brightness in the sky is extremely muted, to the extent that it could go unnoticed.
Civil Sunset is another term of interest. It is represented by the time difference between the exact moment of sunset and the designated civil sunrise time. This is because civil sunrise is defined by a point on the horizon, not by actual sunrise.
In the same vein, the concept of Actual Sunset is characterized by the time difference between the exact timing of sunset and actual sunrise. This is essential to understand as actual sunrise and sunset times can vary from calculated or measured times due to variations in atmospheric conditions and geographical locations.
Worth mentioning is that the fluctuation in daylight duration from one day to another, when available, is also brought into cognizance. This not only helps in anticipating the amount of natural light available for certain outdoor activities in the near future but also aids in understanding the patterns of seasonal daylight changes.