Sunrise, Sunset...Dawn to Dusk

Not long ago I became interested in the schedule of the rising and setting sun at various times of the year and in different places. What I didn't realize is that there are two other periods associated with the rising and setting sun that are equally or even more important than the actual sunrise and sunset. These are the periods before sunrise and after sunset which we usually refer to as "dawn" and "dusk" but are technically grouped under a category called morning and evening twilight.

The twilight hours are further characterized by the amount of degrees that the center of the sun is below the horizon. The first of these, Civil Twilight, is the one that most people are familiar with. One important feature of Civil Twilight is that it defines our laws that govern illumination such as street lights and automotive headlights.

Civil Twilight is the time at which the the geometric center of the sun is between zero and six degrees below the horizon. At this point, there is enough light for objects to be clearly distinguishable and that outdoor activities can commence or end without artificial illumination. Civil twilight is the definition of twilight used by the general public.

Nautical Twilight is the time when the center of the sun is twelve degrees below the horizon, and only general or vague outlines of objects are visible. During the evening this is when it becomes too difficult to perceive the horizon, and in the morning this is the point when the horizon becomes distinguishable. This term goes back to the days when sailing ships still navigated by using the stars.

During Astronomical Twilight the center of the sun is between twelve and eighteen degrees below the horizon. Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening the sun does not contribute to sky illumination. In fact, for a considerable interval after the beginning of morning twilight and before the end of evening twilight, sky illumination is so faint that it is practically imperceptible. However, this period is very important to more than two billion people around the world for it announces the arrival time for a fasting to begin. It is even mentioned in the Qur'an:

"Eat and drink until the white thread becomes distinct to you from the black thread of dawn"
The Holy Qur'an, Surah al-Baqara, verse 187.

In Spanish there are several vocabulary words used for dawn and dusk:

dawn - amanecer
very early in the morning - de madrugada
daybreak - al alba
twilight - crepúsculo,  las horas del crepúsculo
atardecer - dusk
tardecer - to grow dark
anochecer - nightfall
oscurecerse - to become dark
penumbra - semi-darkness

My favorite Spanish word for daybreak is "al alba". The word "alba" comes from the Latin word "albus" meaning white. Words in Spanish that end in "a" are generally feminine gender but "alba" is actually masculine gender and thus "a el alba" becomes "al alba". It describes the longing of lovers who, having passed a night together, must separate for fear of being discovered by their respective spouses. It is related to the Old English "aubade" which is a morning love song or poem about lovers separating at dawn. An aubade is the early morning equivalent to the evening serenade.

In English Literature the sunrise and sunset are described in countless ways. For sunrise one of my favorite poems is "The Road to Mandalay" by Rudyard Kipling. Here is the first stanza where the sun rises abruptly:

By the old Moulmein Pagoda, lookin' eastward to the sea,
There's a Burma girl a-setting, and I know she thinks of me;
For the wind is in the palm trees, and the temple bells they say:
'Come you back, you British soldier; come you back to Mandalay!'
Come you back to Mandalay,
Where the old Flotilla lay:
Can't you hear their paddles chunkin' from Rangoon to Mandalay?
On the road to Mandalay,
Where the flying fishes play,
And the dawn comes up like thunder
Over China cross the Bay!"

My favorite poem about sunset, that I memorized in High School and can still recite from memory over four decades later, is "Elegy Written in a Country Churchyard" by Thomas Gray. Here are the first two stanzas where the light just fades away:

"The curfew tolls the knell of parting day,
The lowing herd wind slowly o'er the lea,
The ploughman homeward plods his weary way,
And leaves the world to darkness and to me.

Now fades the glimmering landscape on the sight,
And all the air a solemn stillness holds,
Save where the beetle wheels his droning flight,
And drowsy tinklings lull the distant folds;"

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