Understanding Twilight: The Phases of Dusk and Dawn
Twilight refers to the period when the sun sits no more than 6 degrees beneath the horizon during sunrise or sunset. During this time, conditions are such that the horizon is sharply outlined, allowing the brightest stars to be visible in a clear atmosphere devoid of moonlight or other artificial sources of light. This stage of twilight permits individuals to engage in regular outdoor activities without significant difficulty.
The Next Phase: Nautical Twilight
Nautical twilight occurs when the sun is positioned between 6 and 12 degrees below the horizon at either dawn or dusk. At this stage, while objects may become discernible without electric illumination, engaging in typical outdoor tasks might prove challenging without supplemental lighting. The horizon remains sharply defined, establishing a semblance of visibility even as natural light begins to wane.
The Faint Light of Astronomical Twilight
Astronomical twilight marks a period where the sun dips between 12 and 18 degrees below the horizon during sunrise and sunset. In these moments, sunlight no longer enhances sky brightness before morning breaks or after evening falls. The initial phase of morning astronomical twilight and its conclusion at night yield almost imperceptible levels of violet light illumination; thus, it may even go unnoticed by some observers.
Measuring Daylight Duration
The length between civil sunset (when artificial lighting starts becoming essential) and civil sunrise offers insights into day duration within these phases.
Assessing Actual Sunrise and Sunset Times
The actual times for both sunrise and sunset represent more specific measurements that allow for an accurate understanding regarding daylight hours available each day. Current variations in daylight length can also be tracked daily for deeper insight into seasonal changes affecting our environment.
