Thursday, November 19, 2009


I posted this in December 2008, but I felt the need to post again! Enjoy!

"Twilight" (1820) by Caspar David Friedrich

I have something I need to get off of my chest. I have always been interested in "Twilight." Please do not let my wife know, she will never let me live this one down. Although, she reads my blog and will most certainly find out, please DO NOT let her know. It could damage the town. Twilight is very interesting to me. It even reaches farther than we know, even into other planets. and galaxies. That is how far reaching "Twilight" is.

There are many versions of "Twilight." My wife has all of these on our bookcase. I see them every day and wonder which version is best. Technically, there is only one truly defined "Twilight", but there are three established and widely accepted subcategories of twilight: civil twilight (brightest), nautical twilight and astronomical twilight (darkest). Civil twilight begins in the morning when the geometric center of the Sun is 6° below the horizon and ends at sunrise. Evening civil twilight begins at sunset and ends when the center of the Sun reaches 6° below the horizon. Nautical twilight is defined as the time beginning when the geometric center of the Sun is exactly 12° below the horizon and ending when the sun's center is exactly 12° below the horizon. Astronomical twilight is defined as the time beginning when the center of the Sun is exactly 18° below the horizon and ending when the sun's center reaches exactly 18° below the horizon. I prefer the version "Civil Twilight in the Morning," but my wife prefers another version of "Twilight."

"Twilight" can have varied durations of time, depending on the latitude of the observer. In the Arctic and Antarctic regions, twilight (if at all) can last for several hours. I know that at my geographic location, "Twilight" can last all night and keep me awake for many, many hours. There is no twilight at the poles within a month on either side of the winter solstice. I am going to enforce this rule at my house, this sounds like a great idea. At the poles, twilight can be as long as two weeks, while at the equator, it can go from day to night in as little as twenty minutes. "Twilight" even reaches the Martians. Twilight on Mars is longer than on Earth, lasting for up to two hours before sunrise or after sunset.

I know that "Twilight" will continue around my house for quite some time, but I guess I should be very grateful that "Twilight" is not continuous. Within the polar circles of Earth, twilight literally lasts for weeks in the polar fall and spring. Poor men. What makes me most grateful is that it could be much, much worse. There is a planet in a distant solar system, the name escapes me, that continually faces its sun. By doing this there is one side that is continually light and the other side is continually dark. Yes! you guessed it. Poor, Poor men, if any there. There is an area on this poor planet, roughly 200 miles wide, from pole to pole, that is in continuous never ending "Twilight." This sounds like a planet that my wife and many of her friends would like to visit, but not me. I will be happy with intermittent "Twilight" here at my geographic location.