The interval during which the sun languishes no more than 6 degrees under the horizon at either dawn or dusk is an interesting natural phenomenon. During these twilight periods, the horizon forms a distinct demarcation, and if atmospheric conditions are agreeable – devoid of moonlight or other illuminating sources – the radiant stars in the skyline are plainly discernible.
In this rather magical span, the average person should still be able to participate in regular outdoor engagements. It is a time that bridges the transition from the brilliance of day to tranquil darkness, or vice versa. The world takes on a unique hue, painting a picture that strikes a chord with the aesthetic appreciation of many.
Shift the focus slightly to a different timeframe when the sun is nestled somewhere between 6 and 12 degrees below the horizon, again at the break of dawn or onset of dusk. Here too, the horizon is crisply defined and contour of objects might make their presence felt, even in the absence of artificial light enrichment. But in spite of this, it’s not quite the optimum lighting arrangement for typical outdoor pursuits.
As engaging as these twilight hours might be to some, ordinary outdoor activities may hit a snag during this period. This is purely due to one reason – the paucity of light. Thus, if one wishes to carry on with such ventures, additional lighting solutions would be necessitated.
Let us now delve into the time period when the sun finds itself between 12 and 18 degrees beneath the horizon during either sunrise or sunset. This is a time when the sun abstains from contributing to the illumination of the sky during the very early hours of the morning or the later hours of the evening.
This idyllic scenario arrives at the start of morning astronomical twilight and concludes at the end of astronomical twilight in the evening. The illumination provided by the sky during this timeframe can be described as being exceedingly faint. In many circumstances, it can even be so faint as to be imperceptible.
When measuring time, ‘Civil Sunset’ is a term used to mark the time when the sun’s geometric center is exactly 6 degrees below the horizon in the evening. Some may deduce it as the ‘end’ of the day – but rather it is the start of the transition between daylight and darkness.
‘Civil Sunrise’, on the other hand, is the exact converse in the morning. It denotes the time when the sun’s geometric center is just 6 degrees under the horizon. This marks the end of night and the beginning of morning twilight, a prelude to the full light of day.
Interestingly, the measurement of time can also focus on the differences between ‘Civil Sunset’ and ‘Civil Sunrise’. This calculation gives us the total duration of twilight. In other words, it measures the time of the day when the presence of the sun is not entirely there, yet not entirely absent either.
Likewise, ‘Actual Sunset’ refers to the exact moment when the sun’s upper edge disappears below the horizon. It is a time when night is about to prevail. Similarly, ‘Actual Sunrise’ is the instance when the upper edge of the sun becomes visible on the horizon, marking the onset of the day.
The timespan between the ‘Actual Sunset’ and ‘Actual Sunrise’ is another way to gauge the duration of night or darkness. As the world spins on its axis, the length of the night and day can vary with the seasons. These ‘Actual’ measurements reflect the real-world experiences of the day-night cycle.
Indeed, the change in the length of daylight from today to tomorrow can be intriguing as well. As the Earth’s position relative to the sun gradually shifts throughout the year, so does the length of daylight we experience. These anticipated changes can also be tabulated and observed when available.