The Issue of Time

As mariners, we rely on latitude and longitude to determine our location on a navigation chart. Aviators do the same. The latitude (horizontal) lines and longitude (vertical) lines on the globe give us the basic frame of reference that is used in navigation.

We don't often think of it, but "Landlubbers" rely on latitude and longitude lines as well. While there are several things that landlubbers need to know based their position on the planet, "time" is the most common. However, before we talk about that, what do I mean by a "Landlubber?"

The word "lubber" has historically been used to describe sailors or dock workers that are awkward, clumsy or "not too bright." Over the years, it has been coupled with the word "land," resulting in the current term of "landlubber." The prefix "land" refers to someone who is not a mariner and knows little about vessels and the sea. Thus, a landlubber is not a mariner.

Back to the issue of time. If you look at a globe, or at a graphic illustration of one, you will see a series of vertical lines. Each of these lines runs from the North Pole to the South Pole. They are called "Meridians" and are evenly spaced around the globe. The "Prime Meridian" is over Greenwich, England and is numbered 000 degrees.

On a globe, longitude lines, or meridians, are spaced in increments of 15 degrees, both east and west from the Prime Meridian. The "180 degree" meridian is on the opposite side of the earth from the Prime Meridian. The meridians east and west of Greenwich, England count up to 180 degrees. The place that they meet is called the "International Date Line."

The International Date Line separates yesterday from today and today from tomorrow. The only time that the date is the same on the entire planet is at the stroke of midnight at the International Date Line (the 180 degree meridian).

Based on the "15 degree" spacing of the meridians, the earth is divided into 24 segments. What a coincidence, there is one segment for each hour of the day. Each time zone is approximately centered on one of those 24 meridians. At noon in any given time zone, the sun is highest in the sky over the meridian that is approximately centered within the time zone.

We all know that it is a.m. before "noon" and p.m. after "noon." Did you ever wonder what "a.m." and the "p.m." stand for? They are abbreviations for the terms "ante meridian" (a.m.) and "post meridian" (p.m.). Given its relationship to a meridian in each time zone, noon is either before or after the meridian. Now you can impress your friends at cocktail parties with that bit of trivia. Of course, this all happens do to the earth's rotation. 

As a kid, when I learned about the earth's rotation, I wondered why when I jumped, I would land on the same spot on earth. Wasn't the earth moving below me? The earth moves at 1,038 miles per hour. Again, I am wondering why when I jump, I land in the same place. I'll bet that I am not the only one that has ever pondered that one!

Until next time, I wish you clear skies, fair winds, and calm seas!