Dawn & dusk: a story of angles
You may have noticed, using the Weather Station ephemeris widget, that the plugin makes a difference between several hours of sunrises and sunsets. These hours all refer to a different time of twilight, the period between full night and full day. To avoid getting lost in all these different twilights, here is a quick explanation.
The twilight is the period of the day between full night and daylight, whether it is morning or evening. When it comes to the passage from night to day, it is called dawn. When it comes to the passage from day to night, it is called dusk. Not very understandable? Here is a diagram that is clearer:
Let us see why and how these twilights (morning or evening) can be divided into three distinct phases …
It is during the astronomical dusk that most of the stars visible to the naked eye begin to appear and at astronomical dawn they start to disappear (for a human observer, apart from any light pollution). This is a period when the center of the sun is located between 12° and 18° under an ideal horizon.
It is during the nautical dawn and dusk that the horizon line at sea is visible and that the stars and planets still visible (morning) and already visible (evening) make it possible for sailors to make an astronomical point. It is a period when the center of the sun is located between 6 ° and 12 ° under an ideal horizon.
The end of the civil dawn and the beginning of the civil dusk mark respectively the appearance and the disappearance of the sun (these are the official hours of sunrise and sunset). The twilight is the period when the center of the sun is located between the horizon and 6° under an ideal horizon.
Again, a diagram is worth a thousand words:
I hope this little explanation will have somewhat bring light to you 🙂
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