Tuesday, January 29, 2019

Which Sunset?

Horizon, Sky, Sunset, Ocean, Water, Sea  I don't know why people say watching television is a waste of time but I watch the type of shows that provide me with new information.  Again, due to NCIS, I learned there are three different definitions for when sunset or sunrise occurs.

The three different definitions actually refer to twilight which is the time when its light but before the sun rises above the horizon. 

In the morning, it's referred to as dawn but in the evening, its called dusk.  What actually happens is the Earths upper atmosphere is scattering and reflecting sunlight to the lower levels. The three twilight's happen because the sun is quite large and it takes time to pass by the horizon.  As stated earlier, there are three types of twilight classified by the angle formed by the sun's elevation.

First is the civil twilight. It is defined as happening when the sun is fewer than 6 degrees below the horizon.  Civil twilight lasts until sunrise.  It is the brightest and often people do not need any artificial light outdoors.  During civil twilight, it is possible to see the brightest astronomical objects with the naked eye.

Second is the nautical twilight is defined as when the sun is between 6 and 12 degrees below the horizon.  It is not as bright as the civil twilight and usually requires artificial light for outdoor activities.  The name dates back to when they used to navigate by the stars.  Furthermore, the United States military uses the nautical twilight time when planning tactical operations.

Finally is the astronomical twilight defined as when the sun is between 12 and 18 degrees below the horizon.  This is the darkest version of twilight and often the light is just beginning to peek through the total darkness.

In addition, the length of twilight is determined by the location the viewer is located on the planet.  The twilight at the equator is much shorter from astronomical to civil than further north at the poles where at certain times, the nautical twilight is much longer.

A side effect of the three different twilight's has to do with the color of light you see.  During the astronomical twilight, since the rays of light must travel further, the light is going to show up as deep violet or blue.  As the sun rises towards the horizon, the colors change to red, orange till it finally looks light.

I hope this explains the different colors you see every dawn and dusk while learning about the three types of twilight.  Let me know what you think, I'd love to hear.  Have a great day.

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