The interval encompassing the moments when the sun is stationed less than 6 degrees beneath the horizon, at the brink of dawn or dusk, is a unique period. During this phase, the boundary between the earth and sky is unmistakably visible to the naked eye. Under prime weather conditions, which lack disruption from moonlight or other sources of luminescence, viewing the brightest stars in the sky is feasible. Day-to-day external operations can still be performed during this phase, without significant difficulty.
The phase commencing when the sun descends further to position itself between 6 and 12 degrees beneath the horizon during dawn or twilight is also noteworthy. During this period, the horizon’s distinction is easily perceived, and the silhouette of various objects may become visible without the need for man-made light sources. However, customary external activities may not be feasible during this span without supplementary lighting.
As the sun continues to shift and finds itself located between 12 and 18 degrees beneath the horizon at either sunrise or sunset, a new stage begins. During this period, the sun ceases to shed light on the sky at dawn or after this point in the evening. At the commencement of morning astronomical twilight and the termination of evening astronomical twilight, the radiance in the sky is extremely dim, and could potentially be unnoticeable.
One distinctive interval that can be observed is the time between Civil Sunset and Civil Sunrise. This is a term used to refer to the period between when the sun disappears below the horizon and reappears, taking into account civil considerations such as the availability of natural light.
Another significant measure is the duration between Actual Sunset and Actual Sunrise. This denotes the time difference from when the sun officially sets below the horizon to when it reemerges. An interesting fact is that the alteration in daylight length between the present day and the next is also noted when feasible.